Personally, I'm not anxious for all that spam to be "cleared" by getting included in the blockchain.
It would be like having the street outside your house filled with trash and considering collecting them inside your house to "clean the street".
Nice analogy, it illustrates how we disagree. Going with the trash theme, IMO the current setup is akin to saying everything people throw away should be dumped and never touched again. Never mind that due to changing market conditions and innovation, some trash may actually be valuable to people if they can get their hands on it - recycling metals for example.
If you remove, by dictate, the ability to process "trash" beyond some arbitrary treshold, you remove the markets ability to correctly value that "trash".