Excepts adds are often sold on a cost-per-click basis so you are causing a transaction with the advertiser for which they got nothing (no visit to their website to at least consider their wares for a few seconds).
Except why whould I care? The rules of transaction between the advertiser and the website owner are their business, in which I have no say except being its victim (er, resource), so why should I cater to their needs? I get appeals to decency, but it definitely does not warrant calling it "theft of service" or "fraud".
But that's not what the GGP said, he said that "anything other that not visiting those sites is theft of services", that is definitely not limited to false clicking ads, but it also includes simple ad blocking.
