You're not wrong, it's kinda like going to McDonald's or Starbucks just to use the free WiFi — yeah you're consuming some of their resources which are intended for paying customers, but as long as you're not a dick about it and hang out for hours during the prime lunch or dinner rush, your presence is costing them nothing extra, or at least not enough to warrant them doing something about it.

I understand that companies are worried about losing business if too many people catch on to adblocking, but the irony is that the more they cry about it, the more people will realize that that was even an option at all (i.e. the infamous Streisand effect will strike again).