No one that supports alignment supports the behavior that's supposedly justified by alignment either.
People just tell stories about player with jerk behavior and blame alignment because it's what we've had. Players will play PCs with exactly the same behavior with or without alignment or TBIF.
Again, my experience has had things that were
extremely specific to alignment that would...well, I cannot say with absolute certainty that literally no one ever could say them without knowingly sounding like a crazy person under BIFT, but it'd be a hell of a lot harder to make it make sense. Again, I have known people for whom having "Chaotic Evil" written on their character sheet meant that
of course saving this orphanage for no pay was a Chaotic Evil thing to do, because they're Chaotic Evil, so therefore the things they do are
necessarily Chaotic Evil. But I already said my bit and checked out when people started saying that it was possible to have "defend the weak" as an Ideal while being genuinely, unequivocally, no-one-could-mistake-you-for-anything-else Evil, so that may be a conversational dead-end.
"You saved an Orc child, Orcs are CE, that's an evil act, you're a fallen Paladin now!" is nonsense under BIFT. Likewise, "defending the weak" by slaughtering anyone who gets strong enough to oppose you is pretty obviously bonkers logic--now, a character could be incapable of seeing the hypocrisy involved, but it'd still be hypocrisy. Both things work completely fine under several so-called "normal" interpretations of alignment, but don't under BIFT.
If the crux of the problem were "bad players are bad," then your argument would have a lot more weight. But the crux of the problem, for a lot of us, is that
alignment itself, by being a universal declaration of objective characteristic, causes problems. If it's an opt-in system YOU use--and you'll have 40 years of historical documentation to draw on if you want to
call your orcs CE or LE or whatever the hell you want to call them--then whatever. But I have absolutely, literally, truly seen people presume that torture is perfectly fine for Good characters as long as you only torture
bad guys, and at the exact same table other people (myself included) who were utterly appalled at the concept of torturing anyone or anything, something ONLY capital-E Evil people would ever use. And no one discussed it, because both sides thought it was so trivially obvious to the most casual observer that it never came up.
That's the problem with alignment. Exactly what others, IIRC including you, have held up as its strength.
It gets people to turn their brains off. Anyone can choose to do that at any time, I agree. Alignment outright encourages it. BIFT doesn't.