Holy hell, Facebook! For a cash-rich company employing some of the cleverest people on the planet, you're managing to be incredulously stupid here. People who aren't qualified to rate sources should not be asked their opinion. If you want peer review, do peer review... But ask-the-audience isn't that. That all said, there is a redeeming possibility here. You could also do an in-house monitored, qualified peer review…
What if Facebook is weighting the votes based on content consumption and interests of users? If that's the case, then it's possible to get some interesting results. We need to be doing experiments like this.
Worthy of experimentation, but not to decide what's shown on my wall.
You probably can get there in the end, but it's probably easier to pay somebody to objectively rank to the political position, and journalistic integrity of major publications.