I think the sign is clever, because it's comparing the un-easyness that some people feel around those groups of people to the fear people have for spiders, and when you compare them, you realise that those groups of people don't really scare you at all, it's all in your head. Witty.
Your friend is lame and clearly clutching at spanners to try and propel their own agenda. Tell them they're being stupid and that stupidness like that is the reason people try so hard to be PC.