Stereotypes exist whether we like them or not and they're always rooted in a kernel of truth. People form stereotypes based on what they see around them, nobody has the time or patience to figure out whether some dude gesturing in the street waving a bible around with a cardboard cutout saying "chemtrails" actually has a good and nuanced argument about whatever he's talking about, we just assume that they're another looney.

Hell, stereotypes are part of the what made us so successful a species today, we'd have been in trouble had our ancestors decided to figure out whether every sabretooth tiger they saw was actually just a kitten who wanted nothing but cuddles and love so the unconscious creation of them is a pretty deeply rooted defense mechanism.