One of the founding principles of the subvertising
movement is that it is using the strength and power of the
corporate machine against itself. A bit like a really nifty bit of
Aikido.
Given that the corporate media is so powerful, there is almost no possibility to express anti-corporate views using conventional means of communication (the debate is still open as to whether or not the internet will provide a completely free arena for intellectual debate...). So it seems that the only way to express these views is to piggy-back on the power of advertising. Some people like to call it a trojan-horse technology.
Alternatively, some people like to call it vandalism.
Still others like to call it art.
To make up your own mind, I suggest you buy a spray can, walk to your nearest Starbucks, and let rip. If you feel guilty, subvertising is not for you. If you feel an enormous sense of relief, combined with a feeling of emancipation, I give you two weeks before you're hooked...