@Marcus & WhatHappened...
Pretty much down with what you said. Sex-positive has to mean encouraging people to have as much or as little sex in their lives as they want (provided it's all SSC, natch).
london's view is okay as a personal stance. Chai's view is okay as a personal stance. My own stance (lifetime virgin) is okay as a personal stance. All of them are compatible with sex-positivity just fine (heck, I actually do consider myself sex-positive, I just don't want any of it in my own life); none of them would be compatible with sex-positivity if one tried and turn them into a general rule.
TL;DR... Virgin shaming is just as sex-positive than slut shaming (i.e., not very).