Not at all. In many ways, it's more enlightened than simply not buying the comic in question, because it lets DC know in no uncertain terms that people have a problem with that one individual, and not others on the team. And since boycotting a product harms the whole team, communicating one's objection to a certain member is better for the group overall.
If DC were to offer a modified purchase of the series in which everyone but Card would be paid, that'd be another story. But consumers have the right to hold their clients (in this case, entertainment providers) to account, and this is simply one way of doing business.
Funny how right-wingers forget to gush about the viciousness of the free market when it's a social discriminator's turn to smell the exhaust.
It is absolutely impossible to live your life trying not to fund anybody who's opinion you do not agree with (And I find it comical liberals find this to be in any way rational behaviour!). You'd have to stop paying taxes and probably stop buying absolutely anything.
I buy books, music and films from people I completely disagree with on much more important issues than gay marriage. Hell, I'm a Burzum fan. If I can enjoy art from murderers I can enjoy it from people who think homosexuals shouldn't be allowed to have pointless titles. I just... really don't care. I don't get why anybody would marry, whether gay or straight.