Any legislation around Facebook and similar is going to look fundamentally different than antitrust law. It's more likely to look like some sort of "consumer protection" suit rather than a monopoly takedown. I don't trust our lawmakers to successfully figure out the incentive structures; they'll likely seize this opportunity to appeal to their voter base. The results might not be what they intend.
Broadly defined, in terms of economics. I don't see much discussion of Facebook with regards to "market competition". It's free to use, tough to argue that prices are being artificially inflated when there are none.
But I also don't doubt that antitrust suits are how legislators want to pursue action against Facebook.
EDIT: The justification I could see is that (1) advertising prices are being artificially inflated, which is tough given that many other tech companies compete for the same advertising dollars, and (2) that consumers aren't receiving fair compensation for their personal data, but even that doesn't seem like a good fit for anti-trust law.
> In my discussions in New York political circles, many see a Facebook antitrust case as a paved road to a Governorship
As a lifetime NYS and current NYC resident, I sure wont be basing my vote for governor on whether they take action against Facebook. I'd see it as an attempt to use the governor position as a stepping stone to federal government. This state has more pressing regional problems to deal with, in my opinion.
The same ones who set the limits on the railroads and oil tycoons, after they abused their power, or on AT&T, after it abused its power, et cetera. This is why we have government.