I'm really thankful I haven't yet had a job where all I'm developing is new ways to force people to see ads. Imagine working on a 'feature' like this for weeks or months, and the end result is simply that people who don't want to see ads now have to see ads.
I did this. I helped build the Air Installer network. I truly regret it. If you look up that name, all you get is people worried that it installed viruses or malware (guess what... it did) and how to remove it. The other results you'll see include the owners trying to sell its virtues. As though it's anything other than a way to exploit unsuspecting internet users for money. I was young and naive, and I didn't think…
As much as people don't enjoy the morals of adtech, you got to experience scale, and apparently highly reliable code whilst early in your career. You can't blame yourself as a self described "young and naive" person for what others did later.