My mixed feelings on secession
When I look back on the civil war we had here in the US, I am of two minds. The first thing that comes to my mind is thank goodness they ended slavery. Sure, without the Civil War, perhaps slavery would have died out on its own eventually. Apartheid in South Africa ended eventually, without a bloody civil war... but it seemed to take forever.
A million people dying in a bloody civil war? Worth it to see the 13th, 14th, and 15th amendments passed and enforced right then and there. But declaring the Union insoluble? A little fuzzier. It's been something of a help in protecting civil rights, as the US Supreme Court was what led the way to ending segregation and legalized racial discrimination.
But in theory? I don't think our union should be insoluble, and I think it was a grave oversight not to establish appropriate terms and procedures for states to leave the US. You don't want it to be something too quick and easy, something that can be decided upon rashly by a thin plurality of the population in a single referendum when emotions are running high, and it would probably take a year or more just to sort out state and federal properties and debts and carry out the actual separation once you were absolutely sure you wanted to do it.
In this day and age, I don't see it being a good idea, for Texas or any other state, but the idea that the United States can only add, and never even theoretically remove, states strikes me as non-viable. Eternal union may sound nice, but eternity is a very long time - and that's what bothers me about the Civil War. For all the good it did in removing slavery, it's made it very difficult to talk critically about perpetual union.
We've seen time and time again in other countries that there comes a time when it becomes necessary for one people to dissolve the political bands that tie them to another, and why can't it be peaceful more often? The dissolution of Czechoslovakia, for example, was carried out quite peacefully.