I'm not a fan of evangelism of any stripe - Poly, atheist, religious, you name it. If it's important to you, and you want me to learn about it BECAUSE of that? Great. I love getting to know people better.
If you instead want to pull me aside and "tell me about <x>" because it's so wonderful and you need to spread the word to the uninformed masses who only need to be shown the "one true way"? Gick. No thanks. I'll learn about it on my own without the proselytizing and make my own decision.
It may result in the same thing (me learning about something), but it really is the difference between "here's what I believe" and "here's something that shows you that what you believe is wrong."