@Snuff: I completely agree that you play better when you know the strengths and weaknesses of those who you play with. That's a given. But if you're part of a clan, why would you need a public MMR for that? Wouldn't your experience in playing with your fellow clan members be what you use to determine their individual skill levels? Furthermore, a single MMR rating doesn't give enough information about your teammates' strengths and weaknesses. Rather, having an option to make your hero progress bars public, to either your contacts or everyone, gives your teammates an idea of what sorts of heroes and roles you are good at, which I think is a much better, and more accurate, system.
I can also agree that, on the one hand, a public MMR does allow players a very broad sense of the skill level of the other members on their team in a match to get an idea of where they might do well. However on the other hand, I can also see this being used by some players as an excuse to abandon matches if they see a couple of players with ratings that are perceived to be rather low and therefore feel they have a low chance of winning, or use this as an excuse to flame them if things go badly.
It is this latter scenario that I am most cautious about when it comes to public MMR, as well as people seeking to try and abuse the determinants of the rating to boost their own. I guess in the end it's not the rating I have an issue with, per se, but the way it would be used. In a perfect world it would be used as a means of objectively evaluating the makeup of your team and using that to best assign roles to each player based on their skill.
But as we know, this community is about as far from perfect as you could probably get, and a public MMR would very rarely be used this way. People like yourself would be unlikely to abuse a public MMR system this way (that much is obvious) but I fear those who seek to use it properly would be in a minority in the community and thus I am cautious about supporting the introduction of something that I feel would be more misused than not.
I don't understand why you're seemingly taking this personally, because I'm not directing (not intentionally, at least) any ill-will towards you, I am merely trying to counter your points with reasons why I feel a public MMR may not be beneficial. I also want what's best for the community, we just have different ideas about what that might be. I don't have any personal agenda in this and I don't know why you think I do.
If a public MMR does get introduced, then that will probably be the end of it. If it doesn't then we can be assured that discussion about it's introduction will continue, so saying that you don't want to back-and-forth about the pros and cons of a public MMR with anyone who doesn't agree with you is, therefore, a bit strange.