Newton's Third Law of Politics
For a glaring example we need look no further than the standard issue bugaboo of abortion. It's one of those politically divisive issues where everyone seems to have an opinion and the lion's share of them tend to run to the extremes. If you are pro-life, you tend to be very, very pro-life and there is little room for dissent among the ranks. Murder is murder, after all, and it's not a subject suitable for the drawing of gray lines or a discussion of nuance. If you run across a potential Republican who happens to be pro-choice, the sad fact is that there simply isn't much room in the rowboat for him or her. Parallel examples of this can be made on the issue of gay marriage and a few other touchstone debate topics.
The Democratic Party, by contrast, has a long history and wealth of experience in operating as a coalition of loosely attached, single issue groups. The secret of its success, it should be noted, is that the various interests rarely contradict each other to the point where civil war erupts over the margins. If your major concern is the environment, the Democrats will provide you a comfortable home with many like-minded souls. But the key point is that there really isn't a big pro-pollution group out there to oppose you. Some folks may rightly oppose excessive regulation of industry, but they're not going to hit the streets fighting for their right to toss empty beer bottles out the windows of their pickup trucks.
Among your fellow Democrats you are equally unlikely to meet a hostile response. Your neighbor may not be terribly concerned over green energy questions, preferring instead to focus his efforts on concerns over racial inequity in our country. Again, the point is that neither of you is likely to look aghast at the other and scream, "You believe in what!?!?" Even if your focus is on pollution, you're unlikely to be a card carrying member of the KKK at the same time. You're far more likely to give a mild shrug of your shoulders to the other person's issue and march side by side with them down to the poll booth and vote the Democratic ticket.
The bottom line here is that, unlike men, all issues are not created equal. They may attract similarly ardent supporters, but they don't all elicit the same level of rage in potential opponents. Social conservative issues tend to run toward the more fire and brimstone, battle hymns of the Republicans, while liberal issues are frequently a Forrest Gump box of chocolates, happily coexisting with one another.
Social conservative issues, in the end, would likely be crafted by Isaac Newton into his first new law of politics: An argument in motion tends to remain in motion. But as you seek to define the limits of the Republican Party heading into the battles of 2010, you'll want to ensure that the motion in question isn't headed toward a very large cliff.