I think it's one thing to tell a pollster "OMG, if Hillary wins Texas should leave the US" and it's another to actually vote for it. And, even if one supports the idea that states should be able to do this, it's still reasonable to argue that it should require a significant supermajority.

Your point about the erosion of states rights is certainly fair. In any case, it's hard to say what "prevent secession" means without the context of the circumstances.