If it does not cost anything to produce a PoS coin then it does not cost anything to attack the network. As a result any PoS coin can be attacked for free
Yet another with no idea how it works. If it can be attacked for free how are those coins surviving? Take a look at Coinmarketcap, the top list is dominated by non-PoW coins. Surely, if its that easy they would've been attacked by now - the incentive is there.
well, sort of. doge, lite coin, and bitcoin are still on top. you can't even count stellar and ripple as they aren't decentralized. paycoin is new, but partially poW anyway.
As far as attacking, yes you do need some stake at least initially to attack a poS coin, so it's not truly free. probably you would need something on the order of a 1% stake. But on the other hand, it doesn't necessarily mean poS will work at larger scales; many have serious concerns about the security model. You are right that the concerns are theoretical as of now.