I take the "extreme" (but IMO correct) view that all proprietary dev work is immoral. This seems clear to me because whatever you build will some day need to be rebuilt in a libre way.
That might not be true if you work at some exceptions, like Mozilla or Open Whisper Systems or FSF, but for 99% of jobs, you're doing a bad thing that's making the world a worse place.
With that understanding, I recognize that I'm pretty much a slave until I can achieve financial independence. If that ever happens, then I can work on things that matter.
So I don't choose my work domain based on what I like or dislike, I choose it based on pay and living conditions. Right now I'm remote and have pretty good pay, so this is ok for now, but I know everything I'm doing is contributing to a great evil. I hope it won't be that way forever.
Selling ads is about equivalent to me as working on surveillance systems or malware. I don't want to do any of those things, but I'll do whatever is legal and pays the best, so that I can someday get back to the business of making computing better for humanity.