I don't think it's inappropriate, but I refuse to do it nonetheless.  There are a few things that could go wrong when doing so, including the original neg being removed while the counterpositive remains (for whatever reason).  I also don't like leaving a positive for someone unless there's a damn good reason, and a wrongly-left negative--even though it's not right--doesn't rise to that level IMO.

OP, there's a lot that's wrong with the trust system we have, and there haven't been any significant improvements in my time here.  Since there aren't any hard rules telling members what they can and can't do, everyone is basically free to interpret the spirit of the trust system as they see fit--regardless of any consensus among DT members or anyone else. 

It's almost pointless debating stuff like this since people will likely continue leaving counter-positives and there aren't going to be any consequences for doing so (even if it were against the rules or even frowned upon).