I couldn't have said it any better, i agree with this, trust system as it is now is terrible. Like you said, one would have to do trades with higher tiered users to get green rating,
I have done trades with hardly any one, yet I have a positive 40 trust, so that statement is not entirely correct.
In my case, I received my trust and my position on default trust, by my ethics and actions in being aggressive against scammers.
I can't tell you how many times I have been told "If you don't like what I'm doing, you don't have to trade with me!". That's not the way I work - if I see a scammer I call them out. I don't just turn my back on someone being raped either. I actually volunteer with the Guardian Angels society in Edmonton. And my real life identity is well known!
"The Only Thing Necessary for the Triumph of Evil is that Good Men Do Nothing"
Edit: Funny but relevant, the Facebook "On this Day" feature tells me I posted this link five years ago today.
http://en.wikipedia.org/wiki/Bystander_effect