I think it depends on what you’re promoting. I run an ad agency and we do mostly Facebook ads, but we only take clients that do something positive with their work. If you’re promoting people or causes that you believe in, it’s rewarding work. I know people though that just push random products on users and they hate it. For me, it’s all a matter of perspective and purpose.
I don't have a big problem with ads on broadcast television or billboards or in magazines. But I don't see how you can feel good about what you do if it requires harnessing the surveillance apparatus of Facebook. Even if you are promoting something positive, doing so on the back of a company like Facebook just feels wrong.