Yea, totally agree with everything you've said about it being defense mechanism, but the behavior tends to manifest in all aspects of our life and in places where it should not. For example, when I'm sitting in bars and where it's reasonably safe I'm still fairly reserved and I get annoyed when the guy to the left or right of me starts trying to make unsolicited conversation. It's not just me either, when I was younger and first started going out I learned pretty quickly people don't like be disturbed around here any more than I do now.