"bad things" is a subjective concept. A former roommate was building a website in the mid 2000 for a dildo company. You probably don't care, but a religious zealot might consider it "bad".

We're gonna make a deal, I'll let you work in ad-tech, and you let me build tool which allow people to shoot themselves in the foot.

Taking a fully relativist perspective on morality is just an excuse to justify taking no ethical stance on anything at all. It's certainly your choice to exist in society this way, but you can't be surprised if people correctly criticize it as selfish, self-serving, and morally bankrupt. At least embrace it.

I work in academia. I will never work in ad-tech either.

Academia is even more of a scam than tech...

But how far are you as an individual willing to go?

- Apple uses exploitative labor practices to manufacture iPhones [0]

- Google is increasingly being recognized as a surveillance and manipulation platform. They have even been caught manipulating elections [1]

[0] https://www.washingtonpost.com/technology/2020/12/29/lens-te...

[1] https://www.judiciary.senate.gov/download/epstein-testimony

Big tech get a free pass because, in the western world at least, they offer their regular sacrifice to the dogmatic left God.