> Graffiti, fundamentally, is a defacement of public property
Both wrong. Neither is defacement the point nor doing it to public property. Fundamentally it's a visual art form and whether that's on private or public property is insubstantial.
It's surely intervoven with anarchic protest and that's where the defacement angle comes in. Similarly, public property as a symbol of the state that is rejected plays often a role. Though that's ironic too since if the "artist" comes from a left-leaning anarchic background then damaging public goods is kinda counterproductive, as opposed to private property of the rich who are the more usual target for symbolizing oppression of the poor.
Both statements are wrong. But yours is wrong-er. You are thinking of street art. Or just spray paint art. The whole point of graffiti is to "get up". If you don't know what getting up is, you should not be espousing any opinions on what graffiti is and isn't.