If you've opened your mouth and made noises about any controversial issue you've met people who assume the totality of your philosophy. Namely, if you say that you're pro-life, people assume that you're pro-gun; if you say that you're pro-choice, people assume that you're for gun control.
Obviously, these issues have nothing to do with each other. The issues are just associated with political groups.
The problem is that those assumptions are usually right. This is the example of human complacency. We try too hard to fit in with a group and be "pure" rather than evaluating each individual issue for ourselves.
Nobody is exempt from this. I'm not exempting myself from this. I just think that it's something that we need to properly evaluate.