Users can add whomever they want to their trust lists although they should be a little more strict if they're DT.
I know DT ain't what it used to be, but any DT member should still be way,
way more prudent about who they add to their trust list
and who they give positive trust to. It's always been an expectation of DT members to demonstrate that kind of prudence, lest we end up with a bunch of unknowns on DT or with green trust that they could possibly scam somebody with.
Just my 2 cents, but this was some seriously bad judgement.