Oh it starts off harmless. "I'll just read a couple", you say. But a year later you're mainlining SSC and pissing off all your friends talking about "virtue signaling". And then a year after that you're living in Berkeley, dating five people, and giving a third of your income to MIRI. Kids, just say no!
Edit: Arguably, this is a better outcome than monogamy in a highly gender-skewed community (e.g. 1 in 2 het men dateless).
50% monogamous, 15% poly.
Every lesswrong group I've visited - in the US, Europe and India - had multiple polyamorous people present and discussing polyamory, so I'd be surprised if this poll is way off.
http://lesswrong.com/r/discussion/lw/nmk/2016_lesswrong_dias...
http://lesswrong.com/r/discussion/lw/nor/2016_lesswrong_dias...
http://lesswrong.com/r/discussion/lw/nqa/2016_lesswrong_dias...
http://lesswrong.com/lw/nx2/2016_lesswrong_diaspora_survey_a...
The one that concerns you is that LessWrong is now 18.2% polyamorous. This might just be an effect of increased scope of survey respondents though.