Spam filters keep out things that 99.9% of people don’t want. Obvious attacks. Those attacks technically conform to the protocol but they are nonsense that nobody (including even the originator) cares about and that nobody is willing to pay for, and so they get blocked despite meeting technical consensus so they don’t disrupt node operations. They have no economic incentive to get into a block, and so they are easily filtered.

Filters are useful for nodes to remain economic against this type of random uneconomic nonsense.

But filters are ineffective against things that have a broad economic incentive, including subjective value.

If someone can get paid or otherwise subjectively desires to get an unusual transaction into a block that meets consensus rules, then they will.

A soft fork could block them (if such a fork could reach consensus), but node spam filters won’t block them.