I think people put signs up like that because there's a culture of anti-fact, anti-science, generally anti-thought growing and becoming more vocal and a sign or bumper sticker might make people feel like they're fighting back. I admire science, I'm aware that part of science is challenging itself and new understanding can unravel previous notion.

I don't really know of any science enthusiasts that want to burn the religious or their texts (well, I did as a teenager, but they grew out of it), but I know more than a few religious who want science out of their schools, deeply believe religion should be more involved in our government, and let's not forget the anti-vaccination movement. These people are neighbors and co-workers, and while they themselves are generally not horrible people those sorts of ambitions feel dangerous at best.

Anyway, my point is - I would rather have a problem with overenthusiastic science fans that could use some perspective, than a problem of people not vaccinating their children and "rolling coal"