To someone with an uncommon interest (a "nerd", in other words, though nerdy interests tend to require higher-than-average intelligence to possess), people with that interest are hard to find.
Once you finally meet someone sharing that interest, and it turns out that they act like a prick, you have a difficult choice (if you value sociable behavior over the opportunity to be social at all; willingly choosing isolation is frequently not a tenable position).
The cost and stakes for confrontation (and exclusion) are higher than it is in a "nerdier" group than for people with more common interests, simply because of the lack of people who are capable of the interest in the first place. So, more bad behaviors are tolerated.
It's also worth noting that "bad" covers both "weird" and "malicious", which is also why groups with these interests tend to be much more accepting of people with other interests outside of those standard for the surrounding society.
The feedback loop is as such less; personality quirks don't get as rounded-off as they would in a less-exclusive group, so any conversions from asshole -> non-asshole in a small community will take longer if they even happen at all.
So, it should be no surprise that individuals more aware than most of the fact that "good people are hard to find" are willing to make certain sacrifices to retain them. For individuals whose interests and abilities involve a larger cross-section of the population, however, people are much more interchangeable, so excluding weird/malicious behavior is much easier.
As an example, consider the tech community's recent trend of attempting to exclude speakers with non-standard political views from conferences. The arguments for doing so come from people with the mindset that technology experts are interchangeable (which is valid in some areas), the arguments against it come from those who see technology experts as an unusually scarce resource (which is valid everywhere else in the world).