This doesn't have anything to do with Hillary or that whole "election hacking" story. If you've followed the hearings and the angles that US legislators have been taking on these companies it seems clear that most of them don't see this as being related to the elections at all.
From what I've seen the focus has been on the fact that foreign nation states are able to use the tools provided by these companies to target groups of people and then directly use the promotion and communication channels provided by these companies to pump propaganda to those groups.
And that this has been done already, specifically to instigate division and confrontation between groups within our society.
Side notes:
1. Maybe you think that their tools don't have an impact on people and this is all just hyperbole. Perhaps that's true, but if it is true then the business model they've been pitching to advertisers seems like hyperbole as well.
2. All of that aside. These few companies have quickly become the dominant gateway for which a majority of people access the internet. It's where they read news, talk to family and friends, organize events, keep all of their photos, keep their contact list, authenticate into other websites on the internet, get tracked by ads and social media buttons across the internet... None of which is inherently bad but it seems foolish for us to not keep them in check. We don't exist to make sure their companies survive. If society decides that the amount of risk and harm resulting from them outweighs the potential good in their current form then we should consider regulation.