While I think this "virtue signaling" is misguided, that does not necessarily mean that the branch renaming accomplishes nothing. For one thing, "main" is two letters shorter than "master" and starts with the same two letters, but that is a rather minor thing. More important, I think, that they ensured that branch renaming is implemented, since that is a helpful feature.
I had previously (not being familiar with git) been concerned that it might cause problems, using the different default name in git and GitHub, but as it turns out this is not a problem at all. I have uploaded a git repository that uses "trunk" as the default branch name to GitHub, and there are no problems at all; it just works.
Also, they did not automatically change existing repositorites. If they did that, that would be a problem too, but fortunately they did not do that.
> No one even knew it came from a Playboy magasine until this whole "retire Lena" movement.
Actually, I think it was well known enough.
Nobody cared, and Lena was generally celebrated in that community, still is in fact. No amount of temporary blogger complaining is going to change that because they completely forget the reason that image is used. It is very difficult to reproduce/compress/etc and while it's certainly possible to use alternative images (though the image provided by the original post is a very poor substitute), it's simply easier to use Lena because people know where the problem areas are going to be if something is awry.