Where will you get the financing for it? Very, very difficult in today's credit environment. Moreover, even if you could get the financing, I'm not convinced the government would approve it without requiring fundamental changes to the route structures and presence in certain markets that will make the combined entity viable in the long-term due to increased competition from lower-fare carriers or carriers in a much better cash position to ride out fare wares.
Unfortunately, I think one of the 3 airlines (CO-UAL-US) will probably go into Chapter 7 bankruptcy by the end of 2009 or early 2010 and be liquidated. Why not Ch. 11, you say? Remember, you have to be able to obtain what's called "debtor-in-possession," or DIP, financing (credit) in order to continue operating while reorganizing the company under Chapter 11. The credit markets are the ultimate arbiters of what's real and what's fiction - at least today. These days, it appears the credit markets are not convinced of much of anything and they're certainly not going to be plunking down hundreds of millions of dollars on a struggling airline in dark economic times.
And if you think you're going to successfully sue the government for saying "no" to a merger or if they reject the ATI application, think again.
Suing government in this kind of case is not like suing the guy who drove through the stop sign and popped you. In that kind of case the burden of proof (simplistically) is "who's negligent?" Suing the government in this kind of case generally involves having to prove that a decision that is otherwise committed to agency discretion was "arbitrary, capricious or not in accordance with law," based solely on record before the Secretary or Attorney General (as the case may be), under provisions of the Administrative Procedure Act (5 USC 701, et seq.). It's a very tall order. Here, my understanding is that DOJ must "concur" in DOT's preliminary decision. If DOJ doesn't sign-on, DOT will likely not be able to approve it.
Monopolies are inherently bad. They stifile competition and innovation, and they hurt employees as much or possibly more than consumers. If there's no meaningful competition, what other options do you have as an employee to realize your earning or promotional potential by making your employer and a competitor raise the ante for your services?
Keep in mind that President Teddy Roosevelt - a Republican and later a Progressive - was the most aggressive president ever in going after monopolies. It was on his watch that the Sherman Anti-Trust Act was passed, the act that DOJ is applying here.
Personally, I hope CO-UAL-US are able to figure out a way to work together so that pilots, other employees and customers can all benefit. Unfortunately, that's a very tall order. We shall see.