One one hand side, I agree that Facebook/Amazon/Apple etc. but also many telcoms are way too big which in turn stifles fair competition and leads to monopolies (and subsequently abuse of power, lobbying etc). On the other, there has not been one good solution proposed to this so far.
Let's run through the options (accumulated over months or years of discussions):
1) Split FB into the FB-Instagram-WhatsApp trio that we used to have in the past. Neat but the main culprit remains the same.
2) Remove Zuck or at least reduce his voting power s.t. the board has more. This would work if we assume that Zuck is the main issue with FB, which I doubt he is. Investors would always push for more money and if it means more of the same privacy-violating, advertising-driven social media, I doubt they would change it - money hardly ever has a moral compass of any kind.
3) Kind of like 2 but on top of this, you fix some members of the board with community/government selected representatives which would be supposed to balance out things and/or at least raise concerns.
4) Introduce point 3 as a general rule - if a company reaches X% of the given industry's estimated total market value, it has to give up some board seats. In theory, forces companies to stay focused instead of spreading into every single adjacent industry.
Now, all of these have problems of their own (corruption in case of 3-4, anyone?) but the sooner the discussion starts the better. Google/Amazon/Microsoft/Apple/chip makers are next in line but also, as another commenter pointed out - we do want to see people build strong and prosperous companies that truly innovate.
Damn, it's a non-trivial topic, just writing this down brings more questions than answers