It would be a very bad idea.
As pointed out in a long article I just posted on my own blog, things are bad and getting worse. They will continue to do so as long as President Obama remains in power. The government no longer has the consent of most of the governed and strong views favoring the sovereignty of the states are far less widely held now than in 1861. Then, many in the South held principal allegiance to their states. Shortly after his state, Virginia, seceded Colonel Robert E. Lee wrote “Virginia is my country, her I will obey, however lamentable the fate to which it may subject me.” He promptly tendered his resignation from the federal army and it was accepted. The same is true of many others, including cadets at West Point. The imbalance of federal versus state power is a major root cause of numerous problems in which the United States are embroiled; the imbalance is also a principal reason why another civil war is not a viable response to those problems.
Neither Lee nor others who resigned their commissions in the U.S. Army in 1861 to fight for their states and against the Union were on that account shot as traitors — or even jailed for going absent without leave as would almost certainly happen now. I do not know how many members of the current U.S. military would side with a new confederacy; some might try, most probably would not.
The old Confederacy fought the good fight against overwhelming odds of men, weaponry and other war materiel. Superior generalship, particularly in General Lee’s Army of Northern Virginia, was not enough. The odds facing a new confederacy would be far worse. Tanks, long range missiles, aircraft, satellite surveillance and the whole panoply of modern weapons would be arrayed against her. They might be used with regret, but used nonetheless. The outcome is as horrible to contemplate as it is obvious.
The United States have the best constitution ever written; we need to protect and defend it as citizens bound, as well as protected, by it. Leaving the union is not the solution; we can be more effective from within than as outsiders and the Constitution deserves and needs all of the protection and defense we can provide.