Untargeted ads are still a security nightmare. Why would I permit loading and executing scripts / resources from arbitrary domains? Ublock is layer 0 defense against malware and viruses.
Why would an ad need to run a script, use meaningful resources or even be from arbitrary domains?
Those are all practical arguments, but the point I'm making is that advertising doesn't have to be this way; it's the implementation that's the problem, not the theory.
