If Facebook is promoting a certain candidate or party, then it can run afoul of campaign finance laws. If it is shown they are acting in a political manner, they open themselves up to being prosecuted for illegal contributions. If they are running ads, for the benefit of political entities it is clear cut that they are making in-kind contributions to the political entity. If they are suppressing one side of political speak it is less clear cut, but the same argument could be made. How much is exclusive advertising worth? The value in the commercial world is real. A bank could sign and exclusive contract with the local newspaper to be the only bank that runs ads in the newspaper. This generally requires significantly more money than a normal ad buy, since the newspaper is forgoing the opportunity to receive ads from competing banks.