I don't care whether copyright assignment is given or not, my objection is to anything getting in the way of improving Clojure. Somewhat frequently you see people come into the IRC channel with a simple bugfix being told their fixes can't be used right now. Often they never get around to resubmitting them once the paperwork has landed. First impressions count for a lot, and I suspect the initial brush-off leads to people being less likely to contribute when they do have something more substantial they could do.
Of course, in the case of Clojure copyright assignment is hardly the biggest impediment to getting patches applied, so maybe this is moot. It is interesting to note that Clojure has only had 33 external contributors since switching to git in the middle of last year, while my own project Leiningen has had over fifty despite being a younger, much lower-profile, and less interesting project:
