Problems: * vetting ads costs a lot of time (= money). So you're getting less money per impression * requires a massive amount of infrastructure if you want to ensure that the ad doesn't change in between you vetting it and you serving it to your clients (= money).
Meaning the consumers of our company will get less money per ad they show to their visitors.
So they'll go to one that offers more. Simple as that.
In order to fix the bad actors we need to start making the websites serving the ads (like Reddit) and/or the networks (DoubleClick) responsible for what they offer up.
As long as that doesn't happen it'll remain a cesspool.