Just what the title asks. Frankly I don't care for cryptocurrency as a "Investment"
The whole thing that gives it its security is the number of systems hashing the blockchain and working through it. That almost ever-increasing number of systems ensures an almost perfect level of security against problems like data corruption of any one copy of the blockchain.
So why would anyone want to make it unprofitable and by extent provide a financial disincentive to continue processing that blockchain?
I have to believe there is at least one currency that actually has this thought process at least. IF there isn't then the eventual loss of incentive to mine is a problem by itself that needs to be addressed.