Looking at our foreign policy since Wilson, the number of countries in the world has tended to increase because of it. The U.S. must take the odd position that it's the only indivisible union in the world.
The argument against secession that I care about is it'd just be a pain to replace our domestic affairs with foreign affairs and have the roads and airports be international borders. Texas (like a few other states and regions) is larger and wealthier than plenty of countries and would be capable of negotiating its own trade deals and alliances. That's not really the issue.
Also, is this really going to own the libs? I like Texas a bit more than the country overall, but we have plenty of libs here. What would be more fun is if the libs break away a few states on the coast to do as they please with, then we in the middle can get the "rump United States" bragging rights.
Actually I am pretty sure that 99.9% of countries in the world consider themselves "unbreakable unions"; so the US is far from the exception on that. I believe the only ones that recognize a right to secession are Ethiopia (not exactly a paragon of democracy, plus even when a place did want to secede the Ethiopian army just invaded anyways), St. Kitts & Nevis (a tiny Caribbean island state) and Liechtenstein (a tiny European microstate)
