The Rules of Graffiti according to SHAM: For anybody out there who doesn't know the rules about graffiti, let me tell you: There are none. Some people will say, 'Well you can't go over this and that...' Listen, if it's there, go over it. The more people I take out, the happier I am.
If you're talking about piecing, destruction has nothing to do with it. The writer is doing their level best to paint something pleasing in a neglected place, or somewhere they have permission. Piecing is rarely done on property that someone cares for, so it can't really be described as destructive.
If you're talking about bombing, most writers will acknowledge that they are damaging the property they're writing on. But I don't think they'd sum it up as destructive.
You often get this argument when a writer is prosecuted for painting trains. The train operator will discuss graffiti in terms of "damage" and the financial implications of reparations. Writers will argue that the train is still in perfect working order, and refute the claim that the graffiti is a negative addition to the façade of the vehicle.
Writers enjoy seeing graffiti when they're out and about, so tags that most people would describe as sheer vandalism take on a different, more positive, demeanour. Writers are thinking about giving other writers something to look at, they're not worrying about the guy who's cleaning the shutters or wall. They know it's frowned upon, but they don't really think of it as immoral or destructive behaviour, although they do get a thrill from the knowledge that they're acting reprehensibly in the authorities' eyes.
It really comes down to the motivation for writing. Most people see graffiti as immoral, so they assume that the perpetrator was acting maliciously when they painted it. Writers see things differently; the destruction is secondary, the enjoyment (theirs or other people's) comes first.