Rob,
I understand some can get abusive with their comments and we all have different ways of communicating but the bottom line is that if someone doesn't like what is being said just ignore it and move on. I see way too many folks try to control the dialog with comments like "if you don't have anything positive to say....." and I find those types of comments more abusive than any other.
I have learned a lot from this site and much of what I have learned, and value, is from comments that tear a car apart or expose (verified intentional) misrepresentation. It is true that some of the comments can come across as caustic but I would rather hear what the horse has to say directly vs a watered down version. Those that don't like reading caustic posts should just move on instead of trying to control how others communicate.
We already have laws concerning libel and slander and those are applied, many times, to improper statements on the internet and as long as there is no attempt to defame, IMHO, everyone should feel free to speak their mind.