As someone who plans on running for high office someday, I've given a lot of thought to the so-called "social issues" that parties seem to rely on for their platforms. There's many reasons for this, and I'll try breaking a few down to help clear up why such contentious topics are so readily discussed in politics.
First, their contention in its self: A topic such as abortion or capital punishment often has a very easy line to separate sides. People are very easy to paint as either pro or con on these issues, which makes it easy for a party to take a side. If we look at abortion for instance, you'll notice that parties have been taking sides for years on the issue, though once elected, nothing gets done rarely. Even Roe v Wade had little to do with the current government in power, and far more to do with the Supreme Court calling the case up and laying down a monumental decision. If you look at gay marriage and our current presidency, you'll see that Bush has often used a constitutional amendment as a strong basis for his stump speeches, but once in office he's done very little. The amendment makes a great running ticket, but it's somewhat illusory to assume that'd pass the state votes needed and get by the supreme court's decision as well. With a two party system, it makes it easy for a party to grab one side of a contentious issue to oppose the other, which brings me to my second point.
The two party system: Our current political system claims to be open to anyone who wishes to run, but I think most will agree that that's illusory at best. Just looking at number of democrats and republicans compared to independents and third parties in the national positions shows that this is a very two-party centric country. First past the post (50%+1 vote) means that vague, over-simplified voting issues are the easiest to get elected on. When there's more options to vote for, more viewpoints can be put forth and these topics suddenly become more than pro-choice/pro-life. Multiple party systems open up dialog.
Third, public apathy: It's no secret that America doesn't vote. We have lower turnout than most first-world countries. I doubt I'm taking a gamble when I say few if anyone on this board have read their local statutes or a tax law (trust me, there's a reason; they're lame). When it comes to abortion, it's very black and white. Same with gay marriage. But military spending? Public financing? If you listened to a Presidential candidate stand up and ramble on about percentage spending on education or the latest budget summary for the military, I doubt you'd be deeply interested. These make great vague talking points for state of the union addresses, but overall have little merit unless we get into the nitty-gritty. Most of America doesn't seem to want to hear that.
The bottom line is: America wants these issues. As much as we hate them individually, we love them as a collective. It makes election choices easy. When a candidate aligns with our basic beliefs, it makes it easier to assume that they'll also align with our more technical beliefs. Either that, or people will honestly only vote on those issues and not go to the polls if their isn't a candidate who aligns their way (this will be interesting for '08 if the Rep. nominate a pro-choice candidate like McCain or Guilliani).
Hope that helps. Any questions or disagreeables, direct them this way and I'll be happy to talk.
