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.