There’s no reason to use md5 if you don’t care about security and only want speed. Non-cryptographic hashes are incredibly fast to calculate and there are far faster hashing algorithms if you want to go that route. Using md5 is a “I don’t want to think hard” answer, and if you don’t want to think hard, then you might as well be secure in your default answer.

The blame and mistake isn’t honestly on git, but the rest of the tooling ecosystem. This wasn’t a snap decision and the fact that nobody thought to get ready in the 6 god fucking years that this has been planned is the real problem.

This will be painful, but only because apparently nobody was willing to just start supporting it 5min before the deadline.