I agree 100% that people should evaluate trust feedback, but if we were to make a survey asking members whether they even consider engaging in a trade with someone who has a red trust from DT member, I will bet the horse that the vast majority will stay away the moment they see that scary red " WARNING !" before even looking at who gave it and why, therefore we are being unfair to someone who may be very decent and honest with his trades but he got a negative simply for saying something that a mighty DT member does not like.
I think it's the lesser of two (or more) evils at this time. No trust system at all would be quite bad - very difficult to gauge anyone's trustworthiness. No Default Trust and no substitute for it - most newbies would have no clue that the system exists. A small improvement could be to have some prominent message for everyone who hasn't done so to encourage them to set up custom lists. There is still a problem for new users though - how would they know whom to add? If you're interested there is a thread on the trust system improvement ideas:
https://bitcointalk.org/index.php?topic=5080581.msg48500915#msg48500915