Nxt has been running over 2 years and you are now soapboxing the same arguments that have been refuted over and over.  If you think you can easily attack it we have a testnet and plenty of people who would gladly provide you with all the testnet stake you need.  No hyperbole and no harm done, go ahead and prove your claims.  You might want to read the paper that kushti posted first.  The best that you can probably do is a short-range attack that is still impractical.

I expect that you know blockchain consensus is not a purely technical in nature.  Blockchain consensus relies heavily on economic incentives to influence human behavior, whether you are using PoW or PoS.  In the impossible attack you are imagining, many user accounts would cease to exist, which would clearly indicate to any normal user that they are on a fork.  Its no different that imagining that someone secretly breaks SHA256 and mines a new Bitcoin blockchain that outpaces the existing chain.  How do you think people people would react when their bitcoin addresses no longer have any balance?  The chain would be perfectly valid according to the consensus rules.  Would everyone simply shrug their shoulders and accept the loss of all their BTC?