In my opinion is that the issue is feeding data into a monolith that knows you better than you know yourself. The amount of data they have for everyone allows them to create profiles and find similarities that can predict proclivities that you don’t know about yet.
There’s nothing wrong about enjoying the conveniences of being recommended things you’re interested in, but this also means that they can sugeest things you didn’t even know you wanted (and probably wouldn’t have ever have wanted.
Combine that with the fact that this doesn’t just stop at product placement. It becomes all to easy for a malicious company to feed you news and opinion meant to make you feel a certain way or sway your opinion. It gives corporations way too much power over the thoughts and opinions you have on a day-to-day basis and makes you powerless against them.
And before you say, “I’m a smart, well-rounded person and would not be susceptible to those things,” literally everyone is susceptible. There’s no outsmarting them if you play their game. The only way to win is through digital privacy.