1. Too slow transaction times for general use.
2. Too bloated block chain for mainstream adoption.
3. Having to store coins "under the mattress" is a step backwards.
4. Proof of work will lead to too large transaction fees.
5. Proof of stake leads to the rich getting richer.
6. Lack of government support prevents mainstream use.
7. Trading against ordinary fiat currencies causes volatility.
Do you even know how long does it take for a CC to process (Visa) ? You don't obviously.
Have you heard of Satoshis idea of pruning the blockchain? You have not.
You don't have to store anything under the mattress.
The fees can always be reduced, as they already have.
POS is bad, yes.
The point of it is to stay away from them.
That will change with time.
Anything else?