Somehow I don't think the entire community could come up with its own criteria.  For one thing, only a minority would take the time to give their input and/or vote.  Remember when Theymos put the 1-merit requirement in place in order for Newbies to rank up to Jr. Members?  The day that went into effect, I recall quite a few posts from Jr. Members who'd gotten busted down to Newbie rank saying "Why didn't we get to vote on this?".  And the truth is that it was being discussed in Meta for months, and they were all too busy with their bounties to do any reading. 

Another thing is that any community resolution (assuming that it's even possible to get all the voters to agree on anything) isn't going to satisfy everyone.  So unless the rules for leaving trust came from Theymos and were enforced by mods, there would just be more bickering, more drama, and more chaos.  Because if the community somehow agreed to have certain criteria, no one would be forced to abide by it.  There would be counter-negs and counter-positives and complaints and everything else that we already see with the current system.

I would have no problem if Theymos set down some guidelines as far as what DT members can and can't do--but I seriously doubt he's going to step in to regulate the trust system when he's basically taken a hands-off approach thus far.  I suspect he wants the community to police itself, especially since scams aren't even moderated here.