Yes... because if texas seceeds than the other 49 states will all unilaterally band togather against it AND mexico will as well! NOT.
Sure some of the states won't want to commit their national guard troops to the battle but the US Military forces don't need to approval of the states to go in, just an order from the president. That alone would be an overwhelming force for Texas to handle. Mexico may take the opportunity to take Texas back from the US or the drug cartels may move in and wreak havoc in Texas since the US federal government will no longer be patroling the Texan border.
Many states would not want to fight texas at all, some will seceed with it, and mexico will stay safely away, because if it invades the warring us states are liable to pronounce a truce and gang up on it.
And if more states join Texas I said that the entire scenario would change dramatically. The more states that join the harder the fight will be but I still maintain that the US Military will be stronger than any force the seceding states could muster, unless a strong majority of the country joins Texas, but I just don't see that happening.
if Texas feels like it, then who is in their right to tell them what to do with their territory?
The President of the US and congress may not agree with this, especially since there is a fair amount of Federal land (ie military bases, etc) in Texas so it isn't wholly it's own territory.
Last time it happened, it ended badly
And my assertion is that if it was just Texas the US military would be able to end the conflict with little bloodshed. If more states joined in then it would end badly again and I'm not sure who would come out on top.