It's a fallacy to believe that the ability to determine the truthfulness of the content of an ad is binary. 100% or 0%. It's a spectrum. There are obvious truths, shades of gray, blatant misinformation, and everything in between. At the very least, they should clearly disallow verifiably false information. An advertisement aimed at Black voters with the wrong day for voting? That's clearly voter disinformation aimed at voter suppression. How close Facebook gets to the gray areas is by no means an easy problem, but it's patently false to pretend they can do nothing.