I had both versions installed(arch linux). I wanted to remove one of them long time ago, but there are lots of dependencies on python2 in arch (gdb mercurial etc.).

python3 do break many of 3rd-party scripts I am using, so I make /bin/python symlinks to python2. Each python3 update will break these scripts and I needed to symlink python again. So, finally, I removed python3 completely.

These 3d-party python codes are well maintained, but the authors seems not to bother to port them to python3 if python2 is still available.