PoS is not a secure system, it has been demonstrated in the events that we saw with NXT where they even considered a rollback to try to fix the mess that happened with all those exchange hacks. This alone should make you think. The fact they even considered a rollback should raise big alarms.
PoW is still king and will stay king.
The rollback is not done only with PoS, it can also be done with PoW coins. As long as most miner agree, a transaction can be cancelled. This is called hard fork.