Usually only about 10-20% of the coin actively engage in mining PoS.
That in itself is "worrisome" as presumably it means that forks could appear more often.
The other problem with PoS is that those not mining could be in fact colluding to present a new better chain (the cost of doing so being very little as the "Nothing At Stake" point made).
Again it comes down to "distribution" with PoS that basically *cannot be anonymous* in order to be trusted.
I'm not sure where this PoS "collude" concern come from. Who would collude to destroy their own wealth? I hold some peercoin, if you tell me to collude with you to attack Peercoin, I would tell you to gfys. Do you think it's easy to collude with 10,000 peercoin holders? or is it easier for discus fish and ghash.io to collude and gain 51%? I think the answer is obvious.
The fact is forks has NOT appeared more often in PoS, in fact PoW system has had much more forks, including Bitcoin.
Sorry to speak the truth. It is easy to collude with a 10k Peercoin holder than colluding discus fish or ghash.io to gain 51%. Investment made by discus fish or ghash.io is far more than the investment made by 10k Peercoin holder.
Since discus fish and ghash.io's only stake is in their mining equipment, the attacker just has to spend a bit more than that amount of money to buy their loyalty, or if they don't agree, the attacker could just start their own mining operation, yes? that amount is not even 5% of Bitcoin's marketcap.
Now with Peercoin, if you want 51%, you have to buy them, you can't just "collude", since no one will listen you. Now if Peercoin's marketcap is same as Bitcoin, tell me which way is easier?
Well, please tell me 1 BTC = ? Peercoin. Sorry, I'm not into any Alt except Stellar.