It depends why they believe. Irrational faith is harmful, even if innocent. I don't consider having a conversation to be harassment, but for the most part, evangelizing isn't my problem with religion. I expect people who believe certain things to care that other people don't believe those things, when the consequences to non-belief are the worst one can imagine. I just happen to think they are wrong. I'm just as evangelical about my atheism as religious people are about their religion (maybe a little less, I'm not going door-to-door, or standing on a street corner shouting, or going to foreign countries to convince them I'm right).