People accept the risk of the theoretical >50% attack when they use PoW networks.
At the moment there is a similar theoretical risk of a 'Nothing at Stake' attack on a PoS network.
People accept the risk of what a >50% attacker could do to a PoW network if they were a non-rational(economically speaking) bad actor. So why do people dismiss PoS simply because it currently has the possibility of a theoretical non-rational attack?
Seems very contradictory to me.
Except it's not theoretical, and it's not non-rational. Had you bothered reading the links I posted you would have learned that Peercoin was successfully attacked this way.
You don't even need to actually own any coins to attack a PoS coin. You can use coins you don't own anymore, meaning you can't even use the argument "Why would a stakeholder want to destroy the value of his own stake?".