It's been discussed a bit quite a few times without it ever really getting out of hand, though perhaps that's in part because of the ban (people won't go too far into any discussion about it), though I can't seem to find exactly which aspects are banned and which aren't. Essentially it's because you get dumb arguments about what is what tier (usually with different people using different definitions of "tier") and about how useful or useless the whole concept it.
I never really liked the idea of the tier system at first; I think part of it was not wanting to admit that certain classes are "better" than others, which I think is where a lot of people get angry. I think it's important to understand what it's actually trying to say, and also the limitations of that. It's still not a totally practical measure since so many different things can change even within a class (Pathfinder tier lists especially tend to have oodles of "only this archetype" or "except that archetype" entries on them, because many archetypes aren't far off brand new classes) and even "equivalent optimisation" can mean different things in different contexts.
When you actually start discussing specific classes things tend to get a bit more heated - that's probably just people not wanting to admit that their favourite class isn't the "most powerful" (not actually what it means, I know) or other people wailing on something unfairly.