Thick skin
Yes, you have to learn to grow one if you are going to post in very public forums.
I've often wondered how people like Hilary Clinton or George Bush deal with the absolutely rabid attacks against them. I suppose at some point you start ignoring your detratctors. Which, if you think about it, isn't very healthy for the American political system. Maybe it's time we start offerring debate in our high schools again, or at least start teaching basic principles like attack the ideas, not the individual.
The other thing that amazes me is that people seem to believe that others are going to be swayed by the vitriol and hatred they spew. My mom used to say, "you catch more bees with honey than vinegar." (Obviously this makes more sense to a farmer who needs bees to pollinate his/her fields, than to a city dweller who's disinclined to be stung.) I think that motto ought to be posted on all online discussion forums!