I see no reason why fees can't pay for a pretty hefty pow network when there's no block reward but thousands of transactions a second and $30k-$70k coins. Any artificial scarcity on this front now will strangle Bitcoin.
Start with there is no "thousands of transactions a second and $30k-$70k coins" as of now, in reality y' know..
No, now there's block rewards paying for a pretty hefty and oversized pow network.

You not happy already freely spamming a network that takes a difficulty of 60,813,224,039 and 456,026,187 GH/s?
Show some gratitude young man, now where is the mass adoption thing kicking in again?
What? Please explain.
Edit: Ah, I forgot. I'm in the wrong forum.