Visually seeing ads is usually not the biggest problem, although there are issues with too many ads (bandwidth, bad UX) and the security risk of malicious stuff embedded in ads.

The issue (for me), and I think for many people, is the quantity and nature of the data that is collected, and the total lack of oversight for its sharing and usage.

Also, no company will ever remove you from the tracking/data pool just because you're a paying customer. Why would they? Now they can extract revenue from you in two ways!