Ads, tracking, and SEO content: promote low-quality information, allow all kinds of bad actors to profit from bad behavior, promote the use of adware, give economic advantage to actors who have access to big data, create market assimetries, waste my time and attention, make me stressed due to the need of locally filtering barrages of bad, dangerous, or malicious information targeted at me, put my wellbeing in danger because bad information is targeted at people around me that have influence over my everyday life.
TLDR: The ad industry promotes shit content, finances fake news, and wastes my resources.