"When in the Course of human events, it becomes necessary for one people to dissolve the political bands which have connected them with another, and to assume among the powers of the earth, the separate and equal station to which the Laws of Nature and of Nature's God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation."
Sound familiar? If the colonists could declare their independence from England in order to form the United States, then wouldn't it be hypocritical to say that the states can't do the same? Additionally, while there is nothing in the US Constitution that specifically grants the states the right to secede, the ninth and tenth amendments can be interpreted to allow the states the option to secede.
Amendment IX - The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.
Amendment X - The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
Whether it is a "good idea" or not is up for debate. Just look at Colorado and the legalization of recreational marijuana and its conflict with federal law.
Texas v. White is open to interpretation:
http://www.texassecede.com/faq.htm#texvwhite
I once read somewhere (I can't find the source) but both Texas and Alaska could be self-sustaining within five years if they were allowed to peacefully secede from the Union. We already have the infrastructure - where Alaska is limited to a degree (I lived there from 2007-2011) in its infrastructure - so I think Texas would make a faster transition.
The Texas Constitution does state: "Texas is a free and independent State, subject only to the Constitution of the United States." Not the President. Not Congress. Not the Supreme Court.
Economically, Texas can survive. We've done well on our own during this recession (2nd Great Depression?). The real question is a question of loyalty and patriotism. But when the government continues to turn its back on the will of the people and continues to morgage our futures into the hands of foreign governments with monstrous debt that is now THE number one security threat we face (according to Obama's own chief of staff), perhaps it is time to reconsider our loyalties.