I'm pretty much a tell-all kind of person. I understand TMI most of the time, but I don't really feel much of a need to hide things. What's the point? It'll all come out sooner or later - might as well be sooner.
I don't see much of the other guy's situation - only your version of it. I do know if I was arguing with someone and they brought up a ridiculous point (say, someone giving me a hard time for getting laid off, only to know they'd been fired half a dozen times), you're damned skippy I'd bring it up. If someone I'd known had DUI's or been in jail - I'm not going to listen to their "advice" on how much I can drink. I've done that. It's not bringing up the past - it's shutting up a noseybody. I had a girlfriend a long time ago with a history of self-mutilation, attempted suicides, drugs, abuse and promiscuity - lecturing me about my little sister's problems. I let her have it, because it was none of her damned business.
On the other hand ---
Bringing UNRELATED sh!t just because you can is just plain dirty. Poking around in people's past just to be nosey is the product of an insecure control freak.
I think, in a good relationship, you reach a level of trust where it doesn't MATTER how much they know - and as they learn more - it doesn't bother you, either. Heck, this past Thanksgiving my dad told me stuff about his growing up that I'd NEVER heard before. And I thought I knew all of it.