Wiretaps

Help me out a little bit here. The President is urging the Congress to pass a version of a bill that will retroactively make telecommunications companies immune from prosecution for assisting the government with wiretaps on us citizens. Today he asserted that their past cooperation was legal and at the direction of the government. So here is my question. Why do telecommunication companies need immunity from prosecution if they did nothing wrong? Isn't this like calling for a bill to make people immune from prosecution for driving the speed limit? It seems to me that the only logic in making these companies beyond prosecution is so that they are protected no matter what the government tells them to do, legal or illegal. Personally, I think that our government already has or has plans in the works to use the telecommunications companies in direct defiance of our fourth amendment rights.