On the contrary, I think having the limit makes sense precisely in this sort of situation. This is a long-standing member of the community, and he's done something not quite right... He's probably not gonna do it again, since it was clearly rejected by the community. Voting this down to -30 would not have made a difference in the effect on the poster.
By downvoting him, are we encouraging people like Aaron to use HN? Because I really don't think that domain-squatting counts as either hacking or productive economic activity ("making something people want", as pg puts it); when it's being done in order to get paid for worthless clicks, it's borderline fraud. Neither does suing companies engaged in productive activity, such as Google and Facebook. This guy is a menace to all of us who are engaged in trying to make a living by making something people want.
And you want to make sure he feels welcome on this forum?
I mean, admittedly, it's not like he's making his living by destroying the reputations of people who are making things people want (like Valleywag), but he's hardly making a positive contribution. If he had never been born, the world would be that much better for the rest of us.
That's a tricky argument to get into... How do you determine who's worthy and who's not? Who has the power? If you let things go that way, the community becomes elitist and reactionary... Everyone should be welcome to post on this site as long as they are willing to abide by the rules: stay polite, articulate, etc.
Neither does suing companies engaged in productive activity, such as Google
While I agree with you on this with regard to the relative righteousness of a domain squatter suing Google, it's worth noting that Google offers a domain squatting service. They are participating in the very activity you and I consider abhorrent (while also doing productive things, too). In fact, Google very likely makes more money from domain squatting than anyone, since they have a very strong unfair search engine advantage over spam domains from any other provider.
"If he had never been born, the world would be that much better for the rest of us." - according to Aaron's like of argument, Mark would not have gotten from him the Facebook idea and the world would be Facebook none the richer? :P