Look, we tell middle and high school (and college) students all the time: don't post stupid crap on Facebook or Twitter because once it goes public you cannot get it back. Any prospective employer or college will, rightly or wrongly, look at your drunk Spring Break photos, or whatever, and decide, this person does not have the kind of judgment or self-control or maturity that we are looking for.
Same goes for a politician. Nobody stole his diary or imaged his hard drive. He sent these pictures (and, really, I don't get that at all) to women who weren't his wife, then repeatedly lied about it until he was confronted with irrefutable evidence.
What this whole thing tells me about Weiner is that he is immature, lacking in self control, dishonest, and disrespectful to his wife. It may not make him someone unfit to legislate, but it certainly makes him someone whom I would not vote for. I want someone with more integrity than that.