By representing itself both as an open platform and as a company with progressive values, Twitter has put itself into an awkward in-between spot and is bound to create such controversies.
They could have just banned him and said "It's a free country and they felt like it."
Instead they're trying to high-road, and it's.. such a mistake.
I was thinking about what you said in the other thread about trolls, and I think you're off-base. Trolls aren't zen master ego busters, they're the self-hating jerks they seem to be. The "zen master ego buster" story is just another layer of the ego trip.