Feel free to try and attack a PoS chain and let me know how successful you are.
That happens all the time. PoS coins have to use (increasingly convoluted) checkpoint schemes to fight 'nothing-at-stake' type attacks.
NovaCoin, for example, just got #rekt by one. And Balthazar is 100 times smarter and better at coding than Dash's trash developer.
It would be such a terrible tragedy if Dash suffered catastrophic consensus failure about an hour before Madoffield's Miami talk starts...
One instance in the history of PoS coins equals "happens all the time" ... lol
I have already explained this several times ITT. One instance of a successful attack does not mean the protocol is insecure. I know of way more PoW coins that have been successfully attacked than PoS coins, does that mean PoW is insecure? No, as I've already explained... NVC has been on its death bed for a while now. It was an obvious scam coin from its inception and never really caught on. Both PoW and PoS coins are vulnerable when there is low participation in securing their blockchains. Attacking an alive and well cryptocurrency, whether it is PoW or PoS, is very hard and/or expensive to do.