I think `curl | bash` is treated unfairly. Whether you `git clone` or `curl` a script, you are fundamentally doing the same thing: downloading and executing code from the internet. `git clone` just feels safer because it is hiding that fact under layers of abstraction.
If I want to run pip, I need to trust PYPA. It's their code I want to run, and I need to download it one way or another. If I don't trust them to keep their domain secure, I don't see why I would trust them to keep their github repo secure.
And the whole point of pip is to download code from PYPI and run it. pip, git, curl|bash, all do the same exact thing in this case. curl|bash just smells funny because it makes it more plainly obvious what is going on.
For pyenv all is needed is to clone their git repository and add a couple of lines to your .bashrc.