After DEF CON spent a ton of money on it.

It does not matter if that individual is wrong, they can take the con for a legal ride costing up to hundreds of thousands in legal expenses. See Hadnagy v. Moss (DEF CON) for a recent example.

Libel.

Once a con attaches a set of actions to an individual, that con can be sued for libel and it would be up to that con to prove all of those actions that individual undertook to defend themselves. So they just wont. Most con's wont even say a thing about banning someone because of this.

You could look at it and think about how we engineer perfection against an imperfect world. TBH, I often look at things in the world and think about this, as its pretty core to how engineering works.

Flip side: embrace chaos, its how things grow to be unique.