I found three takeaways from the article:
1) they don't see ads as unethical
2) the tooling they work on is improving privacy in ads
3) they donate 47% of what they earn to effective charities
I think you engaged with their first point, and I hold similar views to you that normalising these systems of surveillance is detrimental. jefftk does not discuss this issue in 'Why I Work on Ads' or their other defense 'Effect of Advertising'. However, jefftk's point (2) & (3) seem to appeal to me strongly to why I believe they may be doing a net positive.
I think you also didn't give a charitable view to HN comments. The current top six root comments (by kingsuper20 adriand drcongo baby-yoda thrwaeasddsaf kelnos) are are disagreeing with jefftk, some who directly raise a similar point to that which you made