As a current ATC, allow me to chime in a little bit. *DISCLAIMER* I am not simply saying this to protect my job, but the facts are on the side of remaining a public entity.
Privatization will make the system far worse in the long run. Our union recently put out a press release that the nations Air Traffic system is at least 10% understaffed, with a new wave of retirement in the next 5 years (I am aware this is the union saying this, but seeing the stating numbers at various ATC facilities leads me to believe this number isn't too far off). If you turn over the reins to a private company, they will staff it much like they do at current Contract towers, that is, they will have one or two people come in in the morning, one in the afternoon, and one in the evening. That's it. If it gets busy, there will be no second set of eyes in the tower, there will be no one else to accomplish coordination with TRACON or Center. One person doing everything, conceivably with 100+ operations in a single hour. If you think delays are bad now, wait until a private company takes over. Remember what happened during the 2013 sequester with all the delays that came as a result of reduced staffing?
Let's face it. I personally laugh at the idea of a "not-for-profit" corporation taking over ATC duties. Why? Because There is no such thing as a "not-for-profit" in this country. They may market themselves as such, but in the end, it is all about their bottom line.
That said, if we privatize, how long until we see the airlines pay a few extra dollars to the corporation to ensure they receive priority handling over the GA crowd? How long until back room deals occur to allow American to bypass an EDCT or any flow control measure?
ORD, in 2014 the world's busiest airport by aircraft movements, handled 881,933 passengers. Beijing, the busiest airport outside of the U.S., handled 581,773. Eight of the top 10 world's busiest airports are in the U.S., and we do a damn good job as government employees of keeping all those aircraft safe. Do mistakes happen, absolutely, but you will see that in any job.
Fees for use will increase significantly, which would kill GA operations. The US achieved over 9 million departures in 2013 (all civil aircraft), per the NTSB. Admittedly I'm to sure if that is including all IFR/ VFR and all operations from all public airports, as it took a little digging to find these numbers. I'm not sure what the numbers are in Canada, but I do know they are significantly lower than the U.S. I can't help but wonder if that is in part due to the increased fees on GA imposed on our friends to the north.
Privatizing the ATC system in the U.S. is a bad idea. Do costs need to be cut in certain areas, yes. Can we take some of the concepts that work in the private sector and apply them to what we do, of course. But to privatize the whole system is a disaster waiting to happen.