I don't think I would ever be in favor of activity that leads to further centralization. I don't disagree that fragmentation can make things somewhat confusing for new users, but there are some advantages as well. I like to post to smaller communities for the most part rather than the larger ml and world domains. The responses are more focused on the topic at hand, the communities are usually less hostile and hive-minded, and having all discussions on a just a few big servers leads to a the problem of having all of your eggs in one basket (ie. discussions and accounts disappearing when these servers can't maintain server costs, the admins move on to other projects, or just poor maintenance practices.) To me it is worth the effort to cross-post and seek out other communities to find interesting content.