For years, I thought early merging was the morally correct choice, until a friend in my car yelled at me for doing it. He was a very conscientious person, but he was also a bus driver in the city (and thus much better trained in driving through congested areas). I think it's just a matter of education.

Another way to think of it: if you merge early, then the actual correct time to merge becomes indeterminate. Do you merge when you see the sign? Wait till you see a good gap? What if the person behind you doesn't have a gap, and they drive right past to keep looking? It becomes chaotic, and everyone thinks they are getting picked on when someone decides to merge in front of them or passes them. So much wasted anxiety and anger. It's a lot easier (in congestion) to wait until you need to merge, then merge.

In free-flowing traffic, it's a bit different, but the Minnesota page on zipper merging acknowledges that at the end of the article.