But some other sections on the forum like Bitcoin Technical Support, Development & Technical Discussion even meta have much of the newbies contributing in effective way. This proves that also majority of them come here to learn crypto or trade crypto.
It doesn't prove anything of the sort. ~20k new users get registered every month and ~5k become active (create posts). Few of those may end up in technical discussions. The vast majority are useless bounty-hunting shitposting dregs. You only need to open Patrol to see what's going on.
Not that it has much to do with DT. It would be nice if theymos could implement some disincentives for shitposters but for now this needs to be deal with by reporting to moderators and there are many users doing just that.
As far as I know, we don't have any psychics on the default trust, so the fact is we do not know what their intent is until they act, and any judgement before then is subjective and fairly arbitrary. However, you make a good point this has nothing to do with trust, and trust really not need be involved to solve any of these problems since it is a moderation issue, not a trust issue.