Glad to know greed is OK in 2020.
Where else can we now apply this ?, must be loads of things.
Can you imagine the legal chaos that would result if you could just anonymously claim ownership of something\anything without any burden of proof and identity? What exactly do you think the law should do?
The problem is banksy is in a rather unique position of his own choosing, that the law doesn’t cater for. There is a bigger problem of trademark squating that the system tries to prevent, ruling in has favour would have opened up.
The best thing he could do, is license official merchandise where a certain percentage of profit goes to charity (I believe that he isn’t motivated that much by financial gain himself), promote that and leave it to the conscience of the buyer. iirc he has done something similar in the past.
The reality is for everyone that if you want to have the protection of the law, you need to follow its rules, they are not making a special case for him, there is a path in law available to him, it is just he doesn’t want to take it.