I think for me I can roll with a bunch of Sheppard characterizations, but I'd say being an introvert (and shy) defines him a lot. He isn't good with words or feelings, but he has a lot of coping mechanisms and scripts that he uses for work and for recreation (stereotypical guy-stuff like watching football, comics, dorky TV shows). He's very good at becoming physically competent and learning physical skills (running, sparring, freeclimbing, surfing, shooting, flying, etc.) and I think he thinks that should be enough (I have a feeling that in his marriage, he'd keep the drains clean and the lawn mowed but never say "I love you"... er. I may have written that fic.) He doesn't need stuff because what he carries with him is what he can *do*. (And I say this as an tongue-tied shy introvert who thinks that the day I stop learning new stuff is the day I die, so, um, *hands you a big grain of salt*)

So I don't see that his control issues (need for competency) are necessarily a result of being traumatized; it could simply be that he knows he sucks at feelings, but mastery of skills is something he excels at. And from there, you can extrapolate that it's not that he necessarily wants to sacrifice himself, but he is aware that he's the best (most competent) person for the job (though Ronon's not afraid to call him on that and say "you don't need to do everything yourself").

Someone had a theory that I read somewhere that John's just really not that introspective: he doesn't talk about feelings because he's just not that full of them. Not shallow, but more WYSIWYG. I thought that was an interesting (and possible) interpretation.