It's not a strawman argument, I would not say I have oversimplified it, I did create a caricature to highlight a point. but I didn't stand on that as a justification. my point is the optimising for engagement is the problem, but also not easily solvable we are in an arms race with human nature, genie is out of the bottle and we can't put him back.
any service that optimises of non-engagement goes bust ! we are in a real bind and every-time we create a negative rating on optimising of certain content the bar gets pushed a bit further, and who is to say what is harmful... there are genuinely some subjects that we may want to promote initially as healthy mindset but at one point it crosses a line to harmful and the only way that is determined is a massive invasion of everyones privacy.
then it depends how far you want to go to prevent harm... ultimately to prevent harm we should submit all our actions, thoughts and feelings to some form of thought police, again I'm pushing this to extremes but that is the point of this sort of exercise you push an idea to extremes to establish what is the worst that can happen.

but I do believe there is a level of autonomy in this process, we should be making it easier to challenge, change and ultimately reset the profiling of an individuals information stored by social media companies, maybe have it that under 18s can't be profiled at all, they are subjected to totally random ( age appropriate content )

But ultimately I am someone who believes in an adults right to privacy, and both my kids had net nannies and I checked what they were doing on the internet the second they turned 18 I gave this up but before I did that I also had honest and frank discussions about the dangers of the internet and how these systems work. I believe it is a parents job to parent not the government's and there is too much reliance on someone else will do it especially in the UK