I'm torn on that last point.  There are certainly users on this board who I feel deserve their untrusted rating due to the manner in which they make their posts.  It's not appropriate to give someone negative trust if you disagree with a valid point they've made, but if they make repeated deceptive, dishonest or manipulative points, there should be a warning tied to their account in case some impressionable newbies take their words at face value.  There's a big problem in the world right now with misinformation.  Deliberately spreading misinformation can be construed as untrustworthy behaviour.  If someone feels the appropriate response to that would be best presented in the form of negative trust, it should be up to the individual.