By your argument, gay marriage should be a much lower priority. But I think it's just as much a core belief that gays shouldn't be married that it is that women shouldn't have abortions. The difference in consequences may be your own justification for your sympathy towards the pro-life position, and that's reasonable. But gay marriage and abortion are up there side by side as these huge issues to the right wing. Abortions were legal while gay marriage wasn't. They aren't doing these things for the reasons you're imputing on them.