The insanely named "Fairness Doctrine" is not about providing equal time on radio. If it were, it would also apply to NPR, the major networks, and newspapers, almost all of which are biased to varying degrees to the left; it doesn't. This is all about silencing a point of view, a set of ideals. Those pushing for this know exactly what would happen, which is the virtual elimination of the only conservative outlets for news and commentary (not counting the internet, which is decidedly more fair and balanced then the traditional news media. The radio stations, forced to either give over half their revenue-generating programming to "liberal" air-time, or to simply not carry any conservative programming at all, will be forced by economics to do the latter.
I personally don't see how this could hold up in the SCOTUS, but I've said that about other issues (ala emminant domain), and been proven horribly wrong. Even the title, "The Fairness Doctrine" is an abomination against the principles laid out in the Constitution.