I don't understand how this viewpoint can persist now that we have quite a few PoS chains humming along in production: Cosmos, Tezos, Polkadot, Mina, Solana, Avalanche, Cardano, Eth2.

Edit: I suppose what you said is a fair statement; PoS security is different in that it relies on weak subjectivity. In particular, users can maintain security by syncing every X days, where X is based on the staker bonding period, and not accepting long forks beyond X. It's not equivalent to PoS security, but there's nothing really problematic about it IMO. Several years ago, one could make the case that this security model was untested, but not so much today.