Would you consequently say that Free Republic should be forced to print posts from liberals?
If they were controlling 95% of all the communications in this format, I would say "Yes, Absolutely."
Google is a monster that can actually control public speech. They can have a significant impact on elections, and if you've studied your history, you know the reason why the founders included "Freedom of Speech" as a necessary right was to prevent the government (or one of it's agents) from stopping speech critical of the government.
The intent was that the voters be informed, and if you prevent the voters from being informed, you have tampered with the Democratic process.
So long as Free Republic has only a small percentage of all communications, they should be left alone to do as they like, but when they become so large they become a threat to our form of government, it is time to force them to carry dissenting opinions as well.