There are numerous options. One would be a race of seeing who can make adds that can't be blocked vs who can block adds. Another is making other sources of revenue a bigger part of the revenue. You could just block the people from viewing the site but even in that regard it takes time and effort to do that as well, plus it could create some bad will. Another is keeping the site simpler, you had many volunteers before I'm sure you could get plenty again no one made you pay them.
The whole idea though of blocking being stealing is a tough argument. You made choices that had it that adds pay you by being seen and not just having them advertise on the site based on the number of visitors. Your choices of how you choose to set the site up let that be possible, maybe adds pay better of some type of another. I'm sure the ones that swell up and block out the page pay better than others but they also annoy people more. Maybe simpler adds wouldn't pay as much but if you don't have to worry about it being blocked it might be worth it. You took the risks by choosing certain types of adds one that is more risky. Is it stealing that people can block them or just the consequences of the risk you took? A lower income add that couldn't be blocked wouldn't make as much but you wouldn't loose anything since they couldn't be blocked.