new nodes using up resources
Nodes use very little resources compared to mining operations and are easy to set up and maintain.
some clever hackers might find security issues too
Same about Bitcoin and any other open source software. Naturally issues/bugs are coming up, then recognised and fixed.
How is POS/POI not more centralised ?
There's no way to control and manipulate the market in a way one can (possibly) control PoW/Bitcoin.
Give 156 Stakeholders a Stake for small money instead of giving people the chance to get them in a continous period ?
People have the same chance to acquire PoS coins by buying, just like BTC but without requiring (now centralised) mining to secure the network and generate new coins.
Even if the stake to claim with PoW gets smaller over time isn't this a fairer approach even if you want to reward the risk takers ?
No, as those who operate large mining operations control the network there is not much fairness
(hard to define indeed) left. Not to mention Bitcoin distribution, its numbers are known to be - ironically - worse than distribution of major FIAT currencies.
I'm not talking about NEM in particular here as it has not yet launched. Please see NXT for real-world example.
Neither am I against Bitcoin, it has its place & it has
founded this groundbreaking field of technology in the first place.