Proof-of-stake coins lack one of proof-of-work coins most important properties: censorship resistance.

In both consensus systems, a censor is someone that has amassed 51% of the currently available stake (in PoW stake is mining machines, in PoS it is outstanding tokens).

In proof-of-work systems, a censor can be unseated by censored parties allocating more capital to mining machines until non-censoring parties own 51% of all machines.

In proof-of-stake systems, it is impossible to unseat a censor: since it owns 51% of tokens, it will also owns 51% of newly minted units in perpetuity (assuming it doesn't stop censoring and doesn't run into issues that would end up slashing some of their stake).