The GP is the reason that theme parks and roller coasters exist. Without them, parks would not have the money to build awesome new rides, or throw all of these great enthusiast events. Since they make up about 99% of theme park-goers, obviously not every single one is stupid. However, there are a lot of dumb people in general, and they are liable to say extremely stupid things about a topic that they know nothing about, such as roller coasters. And I think that we enthusiasts have the right to have a laugh over some of the more ridiculous things that they say.
Not all good coasters are hated by the GP, or vice versa. However, when I see the GP queue up over an hour for a Boomerang, or when both my friend and my cousin refuse to ride El Toro just because it's wooden, it definitely says something. Also the GP generally has a "bigger is better" complex, or the belief that Kingda Ka is the best ride ever created.
I think that the definition of a GP is someone that goes to a park without very much or any knowledge about coasters or the like. And that's okay, not everyone is as nerdy as we are! And I still think that it's fine to have a laugh at their expense, I would hardly say that we're dehumanizing the GP by making fun of them, or anything like that.