Depends, are we asking Bristol, Liverpool, London and Manchester or are we asking Birmingham? In the first 2 it's going to be majority positive with Bristol being overwhelmingly 95%+ positive because of the Stokes Croft graffiti culture basically being proud city heritage to the point that half the city is caked in it from the floor all the way up to the sky on half the buildings in the city. In London? I think majority positive but maybe close to like 50%. In Birmingham? Negative because it's full of dipshits.
You're asking someone in the UK here though and you have to consider how much Banksy has had an impact on cultural perception of graffiti in this country. Incidentally, Banksy cut his teeth in Stokes Croft which is filled with some of his most famous work, he also was considered a menace at one point, until he infamy turned into outright fame as a national hero due to the left picking his work up positively and helping him along due to the political leaning of it.
When a city lets go, this is what happens: https://www.luckysophie.com/2024/03/ou-voir-du-street-art-a-bristol.html