How sure are you that 100% of all miners and all mining pools in the entire world will honor the agreement not to put such transactions into the chain in the first place?
I don't believe it would require 100% of all miners. A simple majority, a bit over 50% of the hashing power, should suffice, right?
If even one miner somewhere in the world puts such a transaction into the blockchain, how would you suggest the remaining miners handle the situation? Do they ignore that block, or do they accept it and build on top of it?
I would suggest they drop it. That way it wouldn't pay to waste a mined block including such a transaction. Since miners choose which transactions are included in the block, they needed include them in the first place.