Maybe. I wasn't privy to any discussions around making Python keg-only, but my experience with other formulae that are keg-only is that users will force-link keg-only packages into `/usr/local` anyways. What's more, there are probably enough people out there who do just want a barebones Python 3 installation and don't really care if it gets upgraded underneath them, and we'd like to provide that by default.

The Python ecosystem already contains mature tooling on both Linux and macOS for managing Python installations that are isolated from Homebrew and other system-level package managers, like pyenv. In general, I'd recommend using pyenv in parallel with Homebrew; that will get you the best of both worlds.