The point of anti-trust laws is not to punish success, but to police against an entity using their dominant position in one market to take over a different market.
So what about FB replicating all of SNAP and overtaking them rapidly, taking the advertising growth market share they would of had otherwise? Time to breakup FB?
That just means SNAP sucked if it was that easy for Facebook to entice users. They in no way forced people to use their SNAP replica or charged less than SNAP did.
Is Snap actually in a separate market for antitrust purposes? Looks like the same market to me, but of course that decision is always a somewhat arbitrary judgment call made by the antitrust enforcers and court system.
This is an interesting question for two-sided operations like Google and Facebook. Having a near-monopoly in online search also gives Google a near-monopsony in online search advertising. Likewise for Facebook with social networking.
I'm wary of introducing regulation without clear evidence of its necessity. However, there is a reasonable argument that if exploiting a monopoly to gain advantage in an adjacent market can be harmful, then exploiting a monopoly to gain an advantage in an opposing market could be harmful too. It therefore seems reasonable to ask whether the traditional applications of anti-trust principles are still appropriate for these huge modern tech markets.
Businesses too small to have a real point of contact with either Google or Facebook living or dying by the whims (or mistakes) of their algorithms, for one thing.
Prices paid by the advertisers more generally, for another. There are only two games in town, and both of them go out of their way to obscure what you're really getting in return for your money.