But then, even if you accept that PoW is necessary, the OP's larger point is still very true: BTC is an unstable system, due to high mining costs, that requires a constant influx of new money or equivalently, fees to be paid by existing users, in order to keep the system going.  It's an ongoing tax on users.  As such, Bitcoin is unstable and not necessarily an improvement over PayPal (except for the anonymity, which IMO is going away within the next five to ten years).  I see in the end Bitcoin becoming like PayPal, nothing special.