You again forget that Bitcoin transactions are digital messages. It's not possible to prevent people from making valid Bitcoin transactions even if you don't like them.

You can censor yourself and your own mempool if you want, but do not think you're limiting how others transacting in any way.

If we remove the OP_RETURN, people would just put data onchain with more "harmful" way, like many of them are doing right now.

I think we would like to tell everyone that if you really need to put data onchain, use OP_RETURN instead, that's what it's for!

"...what they can to limit people doing things that weigh down the chain unnecessarily— forever"

There's a block size for this reason that limits the size of the chain and the burden of running the node. If we want to make spam even more expensive, we should reduce the block size.