There are different implementations of PoS, some are vulnerable, some are more secure than PoW.
Yeah.
Just because some coins have flaws that have been exploited does not mean that PoS as a whole can be dismissed.
People should be working together to push PoS technology forward as it's clearly superior to PoW. I find it hard to believe that someone could justify the excess of PoW if and when a PoS alternative exists. Other than making an argument for PoW purely out of self interest of course.
Right now PoW is dominant. And there are some PoS currencies like NXT that are progressing well and appear to have a good chance of solidifying their place as the first secure decentralised PoS currency. Time will tell how it plays out, but it's looking good for PoS thus far I think.
It's possible that PoS isn't feasible but so far even for 'Nothing at Stake' attacks, V. Buterin and Come-From-Beyond seemed to agree that there was a theoretical solution. And that seems to be the main issue right now against PoS.
and how pos(One of the implementations) can deal with the situation in OP's thread?
