Turning a complete repository to a shallow one

Apparently we could do it:

git clone --single-branch git.git cd git git tag -l|xargs git tag -d git fetch --depth=1 origin master git repack -ad

Now the repository becomes shallow and all of history is _lost_. It is a feature for those who wants to reduce disk usage, but it's also a gun to shoot at your feet. I'm tempted to ban this case. If I want to reduce disk usage, I should be forced to shallow clone it first, then remove the original repository. I still have a complete repository if I change my mind. And "rm -rf git" is alarming enough for me to think it twice before executing.

Comments?