If pruning is so safe, why aren't 100% of the Bitcoin nodes pruning? Why keep the unnecessary data?
There are three things pruned Bitcoin Core nodes (as of version 0.21.0) cannot do:

Serve historical blocks to new nodes that are trying to bootstrap.
Rescan for old wallet transactions after importing more addresses.
The getrawtransaction RPC for retrieving arbitrary transactions.

Validation (and security in general) are unaffected.