I always wear pyjamas, not for reasons of prudishness, but because I find it uncomfortable (physically, as opposed to psychologically) to wear little or nothing. It's probably something to do with the sensation of having too much skin-on-skin contact with myself, which I don't like very much, but it's unavoidable when you like to sleep in scrunched up positions. Nighties are right out though, because they end up round your armpits within the first ten minutes, giving you the worst of both worlds.

I pass no judgement on other people's sleepwear, or lack thereof, as it's personal decision taken by grownups and those who they might encounter while wearing it.