I personally think smth should indeed be done regarding the fake news, but not to the level of censorship or forbidding them. I've seen plenty of people actually believe some bullshit and, even when made to realize it was all a dumb fake news, they nevertheless retained some of the opinion that had been caused due to it.
Did they affect the elections? Certainly. To the point where they actually decided them? Eh, dunno... The results were certainly close and, no offense intended to americans, but if there's one country that could get the opinion of millions swayed by ignorance and lack of critical thought, the US comes pretty high in the list. But there were plenty more reasons for Clinton's defeat, so I don't think it was decisive or anything.
Still, I do believe they should be forced to be more open about their news being fake, certainly more than a small line of text at the very bottom of their page, or no message at all.