This sound expensive and probably does not net results while making confidential communication far less trustworthy.

I don't think CSAM is shared on the large social networks and the others just won't implement this anyway because it is an unrealistic technical challenge for anyone smaller than large tech companies.

The article is bad. It frames the discussion as a compromise between privacy advocate and "child advocates". That is not really a good case. Privacy of children is pretty effective in shielding them from abusers.