but doesn't being able to leave trust for anybody at any time obliterate the definition of "trust"?
No, you leave trust on anyone.
Anyone else may decide to trust you or not.
If they trust you, the trust you leave will affect the ratings they see.
If it wasn't for the idiotic DefaultTrust, it would be a pretty good system, actually.
For the longest time I was under the impression you could only collect negative trust if you were in a trade and didn't deliver. Ironically, "negative trust" left by a default user over their disagreement with my personal opinions supersedes positive trust left by a non-default user which involved a trade.
Either you moderate it, or you leave it up to the users.
If you moderate it, it's bad because it can be abused.
If you leave it to the users, it's up to you to decide who you trust or not, so people leaving strange trust will be irrelevant.