If you don't want to see anyone's trust ratings (other than your own) outside of 'Untrusted Feedback' then you can add the line
~DefaultTrust to
your trust list.
Be warned that this will (obviously) remove all trust ratings, meaning you may end up dealing with known scammers if you don't check well prior.
Let me just add that this ruins the point of the trust system. A better way would be to type in -*insert name here* in the box to make sure their reps make no effect on the trust you see.
Well, if you're looking for a way to opt out, and I can see reasons for that (what if you don't trade and you're merely here to learn about technical matters? There's a lot of silly drama related to trust ratings and if you don't care then maybe you just don't wanna see them), then it seems like a great way to do this.
Also, it seems to provide a direct and accurate answer to this:
is it possible to turn trust and associated comments off?
Well, it wouldn't turn them off, but it would move them to "untrusted" and make it so that none of the ratings appears when you're reading a thread.