See, there's the problem. The FTC lacks the authority to fine Facebook for "10 years of selling ads", or really, anything outside of behavior they can prove violated Facebook's consent decree. The distinction here is behavior that we disapprove of and behavior the FTC does (or should) have the ability to sanction.
If the FTC can fine Facebook $5B† for a (comparatively) minor violation as a way of expressing the agency's disapproval for all the rest of Facebook's business practices, it can do that to anyone. It can, for instance, fine Apple tens of billions for minor, provable violations as a way of coercing them into cooperating with law enforcement to unlock phones.
Again, I do not like Facebook, broadly agree with 'idlewords testimony before the Senate today that his necktie is more tightly regulated than our industry, and want that to change. I do not think the FTC should be able to make up the rules as it goes, especially not as a way for politicians to showboat.
† or whatever you think the appropriate number is; I'm happy to stipulate that $3-5B is the appropriate range for the fine