I wouldn't say it baffles me, necessarily. The reason human beings do not just stick to the topic or activity for which they have come together, is that human beings do not like other human beings. When they come together to discuss or do something, they're guaranteed to not like the way somebody does it. If they get past that they still will not like somebody's voice or mannerisms or other friends. These kinds of personality politics have nothing to do with the topic around which the group gathers, unless it's a group gathering together around personality politics. Of course such a group would still have the politics. There is no organization, group and movement whose personality politics could not be cured by simply removing all the people from them. In fact I believe there is currently no conflict on the Moon for this reason.

Granted, fandom has the advantage of not being a church. Churches have the great liability that they come together around a new way for people to be, and so they expect each other to actually be that way. Plus they expect their church to be an official mouthpiece of the centerpiece of their life, which is a pretty high expectation. So it seems to me that if we attempts to solve the problem by writing the abolishment of personality politics into the founding constitution of a group, we exacerbate the problem by arguing about who is practicing personality politics rather than ignoring it. And a new church would be born. :^) So remember the key is, "lower your standards."