It's not formal law, but informal warnings straight from congress and who knows what else privately. Ex: The current investigation into big tech poo-pooing FB's acquisitions of WhatsApp & Instagram, who say that under current law that there isn't anything illegal going on, but maybe we, congress, should make that kind of stuff illegal too.

Everyone has learned from microsoft's antitrust trial you want some semblance of a competitor and not look too self serving.

So...nothing that low overhead ethical business practices would make a company uncompetitive.

Yes what you cite has little to do with mergers and acquisitions (m&a) that the parent post was talking about. While the examples i gave were acquisitions that got congressional attention