Seems perfectly reasonable to me. If one really does believe the place to be evil (and not merely bad at what it does), then actions that cripple it financially and make it more likely to go out of business are commendable if anything.

Of course, better yet is to take it up a notch and advocate for other people to also use ad blockers and to help install and configure them. Thankfully, with how invasive ads are, the advertisers are basically doing all the agitprop; all you need to convince someone to use an adblocker today is to show them how websites look with and without it.