well ECC public keys are cheap to generate.

but (a) yes coinjoin multiple-times the utxo you might have to use or other coins clustering obfuscations techniques and (b) if you’re a devs who can’t afford the ~300 sats (or 0.20 GBP) for a single on-chain UTXO you’re free (b.1) go to work until you can afford a 0.20 GBP utxo or (b.2) go to ask nicely to someone to lend you 0.20 GBP to buy an on-chain utxo.

otherwise, go to read the oreilly “accountability” chapter pointed out above, and you will realize that mitigating well spams is an incredibly hard task.

we do not have magical “trusted” third parties who can magically say what is “spam” or not “spam” in bitcoin, as the only source of truth we have is the blockchain itself.

i’m saying all of this without ironical tone, and it’s not like it’s publicly known i've worked for years now on distributed systems.