It's interesting, because there are sources on the internet that catalogue a taxonomy for all manner of fallacious arguments (Wikipedia is one obvious example), but there doesn't seem to be a name for claiming that internet posts written by the people in set A are hypocritical because they presumably-contradict either 1) posts by people in set B happened to appear on the same website, or 2) some hand-waving characterization of the zeitgeist of the site's denizens.
This is clearly fallacious, I don't know why people keep using this technique, and we really should give it a name so that it can be referred to by shorthand. (Any suggestions?)
If you happen to find a person in the set A intersect B, then you've got a case against that individual. But nobody seems to go to that much effort.
It's called the ecological fallacy -- the idea that a phenomenon which is observed (or in the GP's case, totally made up) at the population level can be automatically assumed to apply at the individual level. Stereotypes are a common example of this fallacy.
It may not be a rigorous proof that some individual are hypocritical, but I think it is an indication that it is likely that there are some individuals that are hypocritical.
This is clearly fallacious, I don't know why people keep using this technique, and we really should give it a name so that it can be referred to by shorthand. (Any suggestions?)
If you happen to find a person in the set A intersect B, then you've got a case against that individual. But nobody seems to go to that much effort.