There is no lower form of political life than the single-issue voter.
Doesn't matter if the issue is abortion, or gun control, or gay marriage, or global warming, or immigration, or proliferation of free markets.
It's a complex world, and a complex nation. Lots of decisions about lots of issues need to be made. They're going to be made by the officials we elect. Those officials won't have the luxury of single-mindedness. They're going to have to make decisions about issues that affect you, even if they aren't issues you feel particularly strongly about. To narrow one's scope deliberately to a single issue, at the exclusion of all else, is essentially an abdication of civic responsibility.