People who use adblockers probably aren't people who would click ads anyway. Showing the ads to such people might allow the website owner to leech more money from advertisers, but it wont actually provide any value to anyone. One might even argue that if there were no adblockers, the views/clicks ratio of ads would go down enough to make advertisers less likely to spend so much money on them. Thus ad-supported services might not even make much more money after all.