There are several disparate groups of folks who are what we call "single issue voters".
The folks steeped in RKBA (Right to Keep and Bear Arms) folks are often single issue voters. If the guy is for gun control, of any type, I'm against him, no matter how many other fine redeeming qualities or stances he may have. L. Neil Smith calls a politicians stance on Gun Control, the Vulcan Mind Meld, because it tells you exactly what he thinks about you.
If you have not read the article it's HERE.
So gun control is easy. Anyone who is for gun control is by definition a Statist, and thus is a priori someone who hates and distrusts individuals. And of course that way lies genocide, because, history has proven that it always ends in genocide.
Sorry, make that Democide
The other big single issue is abortion.
When people get into heated arguments about abortion they think that they are arguing about a medical procedure, in actuality they are arguing a question of epistemology. It's a matter of what do we know, and how.
The question is, when does a human being become a human being. That is THE question. If it's a human, than killing it (other than in self defense) is wrong. If it's not a human then killing it is no different that having a wart removed.
Most folks are going to say that it's a human sometime before birth. Go ask a noticeably pregnant woman "so how's the fetus doing today?" Actually, you better not, probably not healthy for you.
On the other end of the scale, a 10 minute old blastocyst can't be considered human by any rational means. Religious yes, which is why I said it's an epistemological question. A blastocyst hasn't even implanted itself yet, and if it fails to do so (which many do naturally) it's never going to even have an opportunity to be a person.
After implantation it becomes an embryo. Those of certain religious persuasions will say it's a human; those of us who are more secular in outlook will say that at most it is a "potential human".
Now here is the question for the "pro-choice" folks. When does it cease to be a "potential" person and become a person? Yeah. I don't know either.
And that is why abortion is hard. If you can not even agree on definitions you can't have a meaningful conversation. You can talk around the edges perhaps, but at some point it comes down to arguing over how many angels can dance on the head of a pin.
Ok, that one is 42. (duh)