This user training gets even worse because git, when refusing to perform an unsafe operation, trains the user to force instead of training the user to fix the problem.

For example, the developer who overwrote the commits in the case in question probably did so after seeing the following error message:

  abort: push creates new remote heads on branch 'default'!
  (did you forget to merge? use push -f to force)

While it mentions merging, the only recognizable command line ("push -f") is for a destructive operation, instead of the operation (pull or merge, depending on the situation) that will actually fix the unsafe condition. Putting an even partial command line in front of a developer is like putting an OK button in front of a non-technical user - they tend to just use it to see if it (superficially) works. When it (subtly) fails, a novice user will not notice, and will just remember "push -f" as the Right Way to Use Git.