There's actually quite an important difference between making an assumption about a group of people who choose to associate and those that are a group because of an imutable characterisitic. Making assumptions about black people? Probably a bad idea, because that doesn't define who they are. Making an assumption about people who hang out with that loud racist guy? Probably fair - since they're making a choice, and that choice tells us about their charateristic, which brings us back to it not being a stereotype, it's an observation. People who hang out with wildly unhigned racists spreading conspiracy theories, are in fact, probably wildly unhinged racists.