The first is the implicit or explicit contract to view ads in exchange for getting to view content. Entering into a contract in bad faith or breaching a contract is both a legal and moral issue. When the terms of a contract are repulsive to me, I have no moral problem breaking them or lying about my intentions. I would let you pay me any amount of money to eat shit without proof and not follow through. You could always try and sue if that ended up being a problem. Generally though I won't enter into such contracts if there's a viable alternative.
The second thing is ownership of the property that's used to view the content. The argument here is that since it's my computer, I can control what my computer displays to me. I know that you have the copyright on the content and the ads, but copyright doesn't stop me from doing what I want with my own private copy so long as I don't distribute it.
So in the end, if you distribute content to me without verifying that I've viewed the ads first, you're putting yourself at risk for breach of contract on my part, and since I find ads repulsive it's a really high risk because it's my computer and I'm going to program it the way I want.
I'll readily agree that the content/ads thing is a problem, and that people deserve to make money for making things. But any fix to this problem is going to be systemic, not based on convincing people to play by the rules when they can easily get away with breaking them.