You're allowed to classify in whatever way you want. The way the psychological community classifies things is subjective. They use a subjective classification system based off observations. They do not perform medical tests. Classification and diagnosis via DSM is not scientific.
I'm not going to classify them however I want to; that's not right. They are classified as they are for a reason, and it's not my place to try and change that unless there is a strong reason to do so (and I don't see any). They're subjective sure, but not without proper lines of reasoning and support from research. It is scientific. Fuzzy? Sure, but that's the nature of what psychology has to be.
I don't think bad behaviour manifesting from mental illness should be excused either.

I don't think you should be friends with anyone whose behaviour you disagree with. It seems to me this entire time you have been classifying some mental illnesses as inherently more forgiveable of shitty behaviour than others based off how severe they are. Why else does it matter to you how "self aware" or "severe" someone's mental illness is? Why would you bring that up in this thread? Why else would you be trying to weed out the fakers? If shitty behaviour is inexcusable no matter what, then why does it matter whether the person blaming their shitty behaviour on a mental illness has that mental illness or not?
I kinda do see some illnesses as more forgiveable than others. In particular, disorders that causes forms of psychosis or full delusions. Essentially, I see different forms of inexcusable. There's a difference between "this is inexcusable, I am going to do X as a result of this. However, come talk to me when you come out of it enough to do Y", and "this is inexcusable, never speak to me again, goodbye". The latter could be result of bad behavior that really has no basis at all. Let's put it this way. Say someone with bipolar disorder punched me in the mouth unjustifiably for something I said. Compare it to the exact same setup with someone with a non-severe personality disorder. Third case, same setup with no mental illness. I am going to react differently, to each case. In each case, inexcusable for sure. However over the long term I am going to respond differently to each. In the first I am more apt to be forgiving. It's not an excuse, but a reason for why it occured, so I might be more inclined to give another chance.
Excuse and reasons are two separate things to me.
Let's just end this portion here then if you simply disagree. No amount of evidence or convincing on my end is likely to change you on this it seems.
I don't really know how to re-explain it

. Essentially, I can't just sit back and watch someone doing something shitty/wrong without trying to do
something about it. It's a huuuuuge part of my nature.
They both are in denial as part of the illness. My BIL at least is in therapy, but he isn't cooperative. My wife can't admit a problem at all.
The many psychologists I have talked with have said this isn't unusual in the least. For some individuals, they struggle to see who they really are at times. They really can't bare the truth. It isn't that that don't want to be healthy, but that they can't. Fwiw, both are SFPs.
Saying they are not trying hard is being judgmental and ignorant, trying to project your experience on others. If we can accept that there are different types in truth, we can accept that they respond differently to trauma and mental illness.
I'm not projecting my experience. I recognize that some individual will never be able to gain awareness of what they do in the moment. It happens. That said, I have a very, very hard time accepting that individuals can't gain awareness of this in the absence of delusions. Reason being, if a psychiatrist gives a diagnoses, no amount of denying from the patient receiving it makes it not true, or go away. It's no different than someone saying "you have cancer" then the patient denying that. It doesn't make it untrue no matter how much they believe it. So, someone being told they have Bipolar disorder, and saying "no I don't", unless they have legimate delusions... they are just denying fact. I can't, and won't forgive someone like that if it results in bad behavior since they would be denying a blunt fact. I can understand someone losing it in the moment, in particular if memory loss is associated with it, but I would still have a very hard time dealing with their behavior, and would be extremely unlikely to associate with them in the first place.
And I have talked with many psychiatrists regarding the use of medication, given that in have 3 children on meds. They all have freely admitted that they are mostly guessing. They don't know exactly what the children have, but they hope the meds will work. And we change meds regularly, hoping for a better result. Each individual is unique and responds differently.
It's the unfortunate nature of the beast. Luckily, they aren't wild guesses, but informed guesses. There is some basis to it.
And why bag on things that are improved by CBT? CBT is about retraining the brain, breaking the triggers and associations that blind us and prevent us from healing. Meds are mostly just a band aid to stabilize people until they can work on themselves. CBT works for many people where meds often do nothing. And your entire dismissal of personality disorders is bizarre. Psychiatrists don't doubt them...
I am not bagging on CBT, it's worked quite well for me over the years. I'm a huge advocate for it, more so than medication actually.
Now I hope my wife will eventually accept her problems and deal with them. My bipolar sis finally did 6 years ago. For her, the meds were necessary, but her progress has all been from CBT. But every psychologist I have talked with has said you can't force people to want to heal. They need to come to it on their own.
If someone doesn't want to heal, I want nothing to do with them. In some individual cases, if they accept a diagnoses, but that's it, that might legtimize it in some ways, as it takes time to learn and see. There sure as hell better be signs of that happening though (however small).