If facebook's actions are illegal now, they are illegal now, there is no ex post facto. Can't talk for the US, but for example the "friendly fraud" could be considered fraud in many European countries, since it brings profit to facebook by inducing people into error. The punishment includes jail time. You do need someone to start a lawsuit, of course, and that's what the judicial system should do when the fraud is repeated. But do they do it? Nope, instead we just have the politicians whine that they need more power. What a surprise.

The reason why FB and big companies in general are unafraid of current laws is that they know they won't be applied. It's a big hassle to punish the rich and the corporations, because people working in the judicial system just don't care about making big enemies. Also it's a pain in the ass because there are two thousand layers of limited liability they have to uncover before they can put the responsible people in jail. It's much easier to focus all the energy on some poor guy selling some weed or a small business not submitting the right form at the right time. Punishing them need zero effort, they can't defend themselves properly and their punishment justifies the work of the judicial system.

Elected politicians should be the one to keep the judicial system in check, but they don't have an incentive to do so that it starts to punish rich people FIRST. In the end the people, by showing support for "more laws" they only get more laws, which will cost more money to the taxpayers and also will make life difficult for the small business while big business won't care and will even be advantaged by them. All this aside from the fact that it doesn't make sense to make another law when there is already a law.