If "enough" (1 large or many small) miners are willing to fill 20 MB blocks of ~0 fee transactions,
Why would they be motivated to do so? If there's no motivation, then the rest of the argument does not stand.
then some bitcoin users will send ~0 fee transactions, and some miners that mine for transaction fees will stop mining, which weakens the security of the bitcoin network.
Why would these ones stop mining? They would still be profiting. I don't get it.
They'd stop mining because they wouldn't be profiting. It would be like if Amazon lowered the price of hot cakes to $0. Some other retailers would stop selling hot cakes.
Increasing the block size limit reduces transaction fees. Eventually, miners are not mining for transaction fees, but mining as stakeholders to maintain the integrity of the blockchain. Only stakeholders mining doing PoW is like a really inefficient PoS.
What's the logic here? If miners are not mining for transactions fees, they are still mining for the subsidy. Either that or it would be a truly altruistic act. And even if it was, they are not proving their stakes at all. They are still proving they have done some work.
As the bounty decreases, and if the transaction fees decrease (as a result of block size increasing), then non-stakeholders will have no (or decreasing) incentive to mine. Stakeholders, on the other hand, will need to mine to keep their bitcoins safe. It's no more "truly altruistic" than a bank hiring a security guard to protect its assets.
How much will a stakeholder or saboteurs need to spend on mining to protect / steal $100 in a PoW system? About $99.
How much will a stakeholder need to spend on mining to protect $100 from saboteurs in a PoS system? A lot less than the saboteurs... Right?
tldr; As we move the direct profit incentives for mining, the responsibility for maintaining the integrity of the blockchain will fall on stakeholders. PoW is a great way to distribute the initial coins, but it's a really inefficient way for stakeholders to "vote" on which chain is right.
Right?