This probably isn't the post you are looking for, however it describes a similar process: https://meaningness.com/geeks-mops-sociopaths
Political topics elicit lower quality participation, holding the set of participants fixed. This is the thesis of "politics is the mind-killer".
Here's a separate effect: Political topics attract mind-killed participants. This can happen even when the initial participants are not mind-killed by the topic.
Of course at the same time, if we call ourselves rationalists, we had better be able to think rationally about topics which are typically mind killers. That's not to say the conversation has to happen here on LW, of course, but if politics intersects with a high-impact area, it's probably worth talking about within the community.
I am searching for an old LessWrong post about something like "Community takeover": The idea that a successful community (Rationalist/AI Risk) could attract people from outside, who would attempt to co-opt/hijack the agenda to focus on something else.
This is inspired by the suggestion by Carla Zoe Cremer (FHI) and Luke Kemp (CSER) that Existential Risk Studies should look into Wealth Inequality.
Thanks in advance
Søren