> So, what are these random scribblers resisting, exactly?
The idea that the city is owned by the uppermost caste of that society.
> There is nothing lovely about seeing all this garbage littering the walls of public buildings and historical finds do not justify this behaviour.
Massive cathedrals to the rich would be erected and made holy, and individuals upon whose back society is build would demonstrate that though entrance is barred to them, they still can make the thing their own.
Nowadays there's plenty of such things in a city that closes its doors to many people that live in said city. San Francisco is a great example of this, where rising costs are pushing anyone not working in tech. Graffiti is an easy way to spit in the face of the rich that are trying to take a city away from you. Clearly, it has an outsized impact on their sensibilities.
To me personally, it sounds really bizarre. I cannot understand this way of thinking, but I guess it's just a matter of cultural differences.
That explains why I see graffiti in all the rich neighborhoods and none in the poor neighborhoods </s>.
I suspect most graffiti doesn't actually have this twisted motivation. It's just selfishness by thoughtless people wanting to advertise themselves, like dogs marking their territory. This intellectual rationalisation is more of a projection by resentful people with a poisonous worldview.