I have noticed a LOT of that on FR. A few of the posters who claim to be 'libertarian' are downright hostile, nasty, and unable to debate civily. I've become persuaded against the libertarian issues with the help of their posts.
I've actually seen it mostly with the your-a-loser-if-you-support-third-parties crowd. They seem to be the FIRST to get angry and unload on people like BA Conservative.