Is that not all
single issues are equal. (And please note that I said SOME, not ALL :) )
Most are matters of wide public policy and justice that affect us all (Bankruptcy bill, Iraq, etc) but a few are deeply personal matters of human rights and equal treatment - the two most prominent currently being "choice" and "gay rights".
When dealing with common prejudices I find it easiest to illustrate the problem by doing a switch so imagine the following 50 years ago.
Dem Partisan to Black Voter: Don't be a single-issue voter - sure Billy Bob may be pro-segregation, but he is pro-union and they might let you into a union someday.
BV: Hey, there is no way I am going to vote for that racist. I hope he eats dust.
DP: You are being selfish. There are plenty of other issues that affect ALL of us - that is politics, he is better than the other guy.
BV: Are you nuts - do you really expect me to vote for someone that wants to keep me a second-class citizen? You are pissing me off.
DP: You are a fanatic.
Etc......
Now I know that there are many here who do not see these issues as human rights issues - but you are wrong, and you have just failed to summon the empathy to imagine what it would be like for Priscilla Owen or Bob Casey to decide, in their great judgment, whether or not you will be forced to carry you rapist stepfathers baby to term against your will.
But whether you believe it or not, if you want to understand the heat that is generated when discussing these `single issues' perhaps you can understand this.
When you tell someone that for the good of the party they should support candidates that want to strip them of their equality, and call them selfish fanatics, you are being personally insulting.