Calculators endanger the development of mental arithmetic skills as well.

And we collectively decided that it's fine, you don't actually need to be able to solve 1234×5678 in your head.

But I am not sure you can compartmentalize the specific skill we can out-source to AI. I would not agree with "you don't need to be able to think in your head."

Indeed, which is why it’s preferable to only start using them after some arithmetic maturity is achieved.

Right, which is why people make bad money decisions in everyday scenarios. People don't pull out their calculator at the grocery store, but they also never had to get good at doing simple math in their head due to the calculator.