Additionally, PoS attackers can have their stake slashed, so they may never attack again. However, you can't slash PoW attackers, once attacked, they will just keep on coming back (no matter how many times you change the hashing algorithm)
And you need to bootstrap your PoS system by enriching a bunch of insiders so that they can validate your transactions. PoS systems are unfit for being the decentralized digital store of value. Bitcoin has the most fair launch any cryptocurrency can ever have. There is no alternative for Bitcoin's use case.
PoS systems can be bootstraped by PoW, so no problem there.
Bitcoin did not have a fair launch either, there was a lot of information asymmetry between the project insiders and the public. Satoshi's stealth-mine of ~1 million BTC for example.
No, if Bitcoin was PoS, Mt Gox would bail themselves out and govern Bitcoin to this day. Early on, Mt Gox was responsible for over 80% of all economic activity on the Bitcoin network, and was by far the dominant holder of coins.
