> 1. It's inconsistent with copyfile

I think it's ok. When using copyfile you can easily check that the destination file doesn't exist, while with copytree it's harder to do the same for *all* destination files. Therefore it makes sense for copytree to raise an error in this case.

> Given shutil's namesake I assume it's supposed to help make python a viable shell script replacement.

It doesn't mean the semantics have to be exactly the same. Actually, many Python users are under Windows where semantics will be different.

> It makes it difficult to use copytree with tempfile.mkdtemp(). If I want to make a temporary directory and copy a folder into it, I need to copytree to a nonexist subfolder then move all the files down a level or resort to other unpythonic hacks.

I actually don't understand your problem. If you are creating a temporary directory, it is empty so there isn't any risk of hitting an already existing file.

In any case, I don't think your arguments are good enough to warrant breaking compatibility with older versions.