This is such an interesting post and I've taken a lot time to respond to this, so I hope my response is useful in some way to you:
I have had to let my values be flexible for so much of my life just to survive. They shift and change to accommodate what it is I need pretty often, actually. And I am OKAY WITH THAT. I don’t think it’s a bad thing. My identity isn’t that I am unprincipled; it’s that I am a survivor. I am adaptable. I’m a realist. I am able to see both sides of the coin in different situations and think deeply and logically about them (which, ironically, often translates to having a lot of empathy and understanding for others.) I can see both the best and the worst in people, and still love them anyway.
You celebrate your identity as an "adaptable chameleon" and a "survivor" whose values are intentionally flexible. While you may like this trait about yourself, that very flexibility is the enabling mechanism that made you capable of infidelity. More importantly, this worldview is currently preventing you from accepting a critical truth: that many people truly are capable of maintaining non-negotiable principles. Until you stop framing your betrayal as the inevitable result of having principles that "shift as the wind blows" and acknowledge that others possess firm boundaries that do not yield to temporary emotional needs, you won't grasp how some people are capable of fidelity. Had your principles not shifted to allow you to pursue something that "made you feel good," you likely wouldn't have crossed that line.
Your central belief that principles are inherently weak or just a personal defense mechanism—that no one is truly capable of maintaining their moral integrity—is fundamentally flawed.
The idea that prolonged observation will eventually show everyone violating their values is historically inaccurate. We have an unbelievable wealth of examples of people who endured unbelievable levels of torture and death simply to maintain their core beliefs.
Consider the Scottish Covenanters who refused to acknowledge the English king, or countless religious martyrs.
If people are willing to endure skin flaying rather than accept a new king, it is perfectly reasonable to assume that many average people are absolutely capable of holding onto the principle of fidelity and not stabbing their partner in the back for momentary comfort or the pursuit of orgasms. 
This sweeping claim that everyone's values are flexible appears to be your own coping mechanism to justify your infidelity. You want to believe that because you were capable of such a profound moral failing, everyone else is too. You must accept that while many people are morally flawed, many others are not capable of this specific betrayal. Where was this flexible morality amongst the Scots as they were being drawn on the rack? Or being sawn in two groin first. (us Brits have a lovely past) 
You argue that everyone is capable of profound moral failings and that principles are merely flexible defenses. This raises a simple, yet critical, question that your worldview must address: Why is it that some people cheat and others don't? If the capability for betrayal is universal, why isn't the act? Do you truly believe the only difference is a lack of opportunity? Do you genuinely think others avoid infidelity simply because they haven't faced difficult times in their relationships or lives? To fully grasp your accountability, you need to deeply consider what distinguishes your choice from the principled resistance of others.
You equate minor moral failings, such as telling a white lie to spare a partner's feelings, with the act of infidelity. This creates a false equivalency and ignores the crucial concept of a line in the sand. I have lied to spare my partners feelings before. I don't think that's a good thing to do on the whole but I don't have a hard line on this. I simply don't believe steaks are as high as infidelity. So yes, I have moral failings but I also have lines I wouldn't cross. I'm struggling to see why that's so hard to accept. 
We can all concede that no one is perfect. Lying to spare a partner's feelings is a moral failing, but it is not morally equivalent to betraying the fundamental trust and commitment of a relationship through infidelity. The severity and impact are vastly different.
Infidelity involves secrecy, calculated deception, and a profound violation of the partnership agreement.
We all have lines. Believing that some people have the strength to maintain the principle of not cheating is not a moral defense; it's a recognition of human will and commitment.
I honestly think you need to address this failure to distinguish between levels of moral harm if you want to grow into a person who would not betray a partner again.
I will concede that the profound feeling of "being seen" and the realization that you were chasing self-acceptance through external validation is a common and likely accurate diagnosis for the underlying struggle.
However, this is where the self-serving narrative must be challenged: your emotional need did not grant you permission to commit infidelity. You used a destructive, boundary-violating action—infidelity—as a disastrous form of self-medication for an internal lack of self-worth. True self-love is not found in a shared fantasy with an AP, but in the grueling, principled work of becoming the person who doesn't betray their deepest commitments.
You claim the "good people/bad people" dichotomy used in recovery spaces stunts growth and that judgment should be avoided.
I don't believe this dichotomy is universally false, nor do I think you can universally speak to what will help all cheaters. You can only speak to what you need. Some people absolutely need a wake-up call to fully grasp the severity and impact of their actions.
You ask if people are "justifying" or "just expressing" their feelings. When an explanation (like the need for validation) is used to minimize the act or deflect accountability, it functions as a justification.
You raise a valid concern about the motivations of people in these spaces—whether they are truly helping or just "exacting justice." If a responder is motivated by vengeance, that language is unhelpful.
However, when I challenge your claims, it is not for the "secret pleasure of putting you in your place." It is because your current thinking—that everyone is morally weak and that infidelity is a minor moral failure—is a hindrance to true growth. The "wake-up call" some people need is a necessary challenge to the intellectual justifications that allow them to minimize their actions.
To truly heal, you must embrace accountability for the deliberate moral line you crossed, not just celebrate your self-described traits of adaptability and survival. 
I’m a few (VERY intense) months in, and I’m fairly confident I figured out the whys— and not just the surface factors. Because I didn’t go looking for an affair, and I wasn’t putting out this carefully curated version of me in order to attract anybody, I felt like my AP saw me exactly as I was, and accepted me. He saw me, sweating and swearing and absolutely struggling in a vast hellscape, and still found me attractive. He thought I was interesting enough to seek out and talk to for hours and hours every day, when it seemed like no one wanted to talk to me at home. And when I told him all about my crazy fantasies of running away to the wilderness to commune with nature and the animals and live off the land, he wasn’t scared away… He participated in the fantasies too. He saw that I was capable of breaking rules and telling lies and doing something as bad as committing infidelity, and still liked me like that.
I felt good enough for him exactly as I was. That feeling is what I’ve been chasing from men all my life. But what I’ve come to realize is that it needed to come from me all along; that it’s self-acceptance and self-love that I need… And I think that a lot of WS are needing that too, and that’s why many of them can’t resist the validation that their AP gives them.
I don't know your partner, but if I were him and read your account, it would likely feel almost romantic. I've read many wayward spouses recount their affairs, and the descriptions are often dripping in shame and profound regret. Yours, however, reads as though you haven't fully let go of the fantasy or truly internalized the magnitude of the pain you've inflicted. I'm not sure shame is your issue. 
The core question is this: Are you pushing so hard against the concept of external shame because you are actively trying to avoid the painful consequences of your choice? Your argument suggests a morality that bends to facilitate feelings of pleasure and comfort. Now that your actions have created the painful, unavoidable feeling of shame—the direct cost of betrayal—you seek to block it out. Allowing you to circumvent this feeling is tantamount to assisting you in escaping accountability. That path is not one of healing and would be profoundly ignoble.
In your attempt to survive I believe you've carved out a worldview best characterized by emotional hedonism. Your approach seems to be governed by a simple, self-serving logic: principles must be flexible if they restrict pleasure, and unpleasant feelings like shame must be avoided. This means that if something leads to a "good time," the principles bend to allow it; such as the affair itself. if a consequence, like shame you feel is being pushed, makes you feel bad, the focus shifts to blocking it out. Constantly shifting your moral goalposts to manage immediate comfort, however, offers no foundation for lasting change. In the long run, this avoidance of accountability will only guarantee the instability that made you vulnerable to betrayal in the first place.
If you feel this lengthy response is meant to do anything other than challenge your current thought process and help you achieve genuine growth, I sincerely apologize. Nothing here was written out of personal pain, but I am sure it can be read that way if you choose to see confrontation over difficult introspection.
 [This message edited by DRSOOLERS at 11:04 AM, Monday, November 3rd]