Glad you pointed this out because I actually considered the argument for a moment. However, Visa blocked donations to a porn actor who opened a donation page for a serious illness (can't remember what). We don't need these companies doing moral-policing.

Hold the ad companies responsible. They are the most complicit.

Or that time PayPal shut down WikiLeaks donations.

The last thing we need right now is some political party declaring their opponents a scam and turning off their donations. Not that I'm a fan of political donations, its just that I'm even more troubled by policies that would give an edge to incumbents.