An added benefit of PoS is that it enables economic penalties if someone tries to attack the network.
A beginner’s guide to Tezos
Linda Xie

This isn’t necessarily the case. Economic penalties can only be used if the validators have security deposits — early PoS algorithms like those used by NXT have no concept of economic penalties.

In the case of Tezos, their PoS algo only slashes on very specific conditions; they don’t slash for other conditions that do/could constitute an attack.

From their white paper: “safety deposit to be forfeited in the event of a double mining or double signing.” However, this may not penalize signing two conflicting blocks at different heights (at least, the original slasher algo they cite from does not), validator-on-validator censorship, etc. Thus, they don’t really take advantage of security deposits to their full extent.