So how on earth do you prove that wifi doesn't cause cancer in your worldview?
Easy. You don't.
The people who believe this aren't looking for proof. They already have all the "proof" they need (in the form of "This is what I think" opinion). Thus, if a scientific study proves them right, they'll tout it as iron-clad proof that they were right all along. However, if a hundred scientific studies find no link, they'll claim the link is there and science just hasn't found it yet.--