It wasn't actually any one thing. But over the past few weeks (months? Years?) it's become clear to me that Debian doesn't really seem to know who or what it's for. Arguments erupt over whether something is a deeply held principle or an accident of phrasing on the website; whether we should release more often or less often; whether free software is more important than our users having functional hardware. And, depressingly, these debates generally seem to turn into pedantic point scoring and insults and yes, I'm probably as guilty as many others in this respect. But it's got to the point where social interaction with Debian-the-distribution makes me want to stab people, even though I've just spent a lovely weekend with Debian-the-people. Perhaps worse, I occasionally find mails I've sent that make me want to stab me.
So it's got to the point where I find myself reading things written by people I respect, and deciding that I'd be generally happier if I didn't read them. I could just unsubscribe from all the mailing lists, except that part of the fun of being involved in Debian was being part of a community. I don't want my only form of communication with the rest of the project to be limited to bug reports, especially when I find the development IRC channels as bad as the mailing lists.
It's interesting to compare Debian to Ubuntu in this respect, though the different ages of the projects make it difficult to draw any firm conclusions. The fairly rigidly enforced Ubuntu code of conduct probably helps a great deal in ensuring that discussions mostly remain technical. The distinction between core-dev and MOTU is a pretty explicit acknowledgment that not all developers are equal and some are possibly more worth listening to than others. And, at the end of the day, having one person who can make arbitrary decisions and whose word is effectively law probably helps in many cases.
There's a balance to be struck between organisational freedom and organisational effectiveness. I'm not convinced that Debian has that balance right as far as forming a working community goes. In that respect, Ubuntu's an experiment - does a more rigid structure and a greater willingness to enforce certain social standards result in a more workable community? In a few years, we ought to have an answer. I look forward to finding out.