Let me start by saying that what Franken is accused of was gross and disgusting and totally out of line. Personally, I don't think it's grounds for him to resign, all by itself. I'd he's still doing stuff like that, I'd say that's different. (Clearly he's not stupid enough to provide photographic evidence these days.)
I've got a couple problems with the idea of this being grounds for resignation. First, I'd be willing to bet he's got plenty of colleagues who've done similar things and haven't been caught. (Yet?) How much effort should we put in to ferreting them all out? Where do you stop? Second, what he's been accused of so far is gross, disgusting, childish, immature, all that, but I don't think it rises the level of being something you could prosecute someone for. (Which sets it apart from Moore.) Do we just throw senators out for gross disgusting behavior related to sex, or will any gross disgusting behavior do? Can we their them our for being childish? (Then most of them are at risk, aren't they?) How far back do we go trying find evidence they aren't fit to serve? Do we leave them a way to redeem themselves? Or does one transgression disqualify them for life?
I can see see scenario where the payoff for coming up with charges like this would be great enough to turn it into a cottage industry. What if the accused actually IS innocent? (Franken's not, but what if?) Does the person get to defend themselves or is an accusation enough?
I'm for an ethics investigation. If he has a track record of doing stuff like this that's ongoing, I'd say throw him out. Otherwise? I think we have bigger issues to deal with.
I've been WAY more surprised about the accusations against Bush the 1st. Franken, like someone else said, has a history of using crude humor. Bush came off as classier than that. (I thought!) I wonder how many presidents we've actually had who DIDN'T engage in gross disgusting behavior?