You have a 5: -0 / +1 trust because you got a positive feedback from Hhampuz, who is a DT2 user.
At the moment that Hhampuz gave me his positive trust, it was marked as untrusted feedback, i had to add it to my trust list so it appeared as trusted feedback, when it was marked as trusted feedback, it started as
1: -0 / +1 until recently went up to
5: -0 / +1, i mean i don't have the green trust after receiving the positive trust of Hhampuz, i had to wait for about 5 months for get it
So your suggestion is already implemented in the forum. I could create 10 accounts and give myself 10 positive feedbacks. But they will be marked as "Untrusted Feedback" and no one would be able to see it (by default).
They'll be seen as untrusted feedback until you add it to your trust list, when you have added it to your trust list it'll begin to up until you'll become a Green Trusted Member,
So the suggestion would be, leave the DefaultTrust and the other users can't add users to the trust list