I appreciate that you think TX's inability to dictate to other states how to run their elections is not a good reason for secession.
And specifically doing it to save Donald Trump's *** is even less of a reason.
What is the case for secession? To a non-Texan left leaning voter, all this talk of secession seems like a kid taking their ball and going home because the other kids wouldn't let them play QB.
That's because you're looking at it through the lens of Texas seceding, and you're generally unsympathetic to their likely reasons to secede. If you take a broader look at it (meaning not specific to Texas), the case for secession is the same as the case for any people seeking independence and self-determination. People want the right to govern themselves (to make their own rules and to define their own culture), and the Constitution generally gives that to states with only a few very specific and very narrow exceptions. Every time that right gets diminished by out-of-state busybodies, by sore losers in that state enlisting the help of out-of-state busybodies, or by economic conditions enforced from above, it strengthens the case for secession.
Obviously, if a state wants to clearly violate the actual words of the Constitution, you can hold that up and say, "you made a deal by joining the union and have to follow it." However, and I recognize how radical this is and don't necessarily endorse it but think it's worth asking, is it entirely fair to hold a society to a compact (the US Constitution) that was agreed to by their ancestors many generations ago? A reasonable argument can be made that at some point, a generation should be allowed to chart its own course.
We look at secession from cultural angles that form the basis for some Texans' desire to secede and garner less sympathy from liberals who have sway over cultural institutions. However, what about economic angles? For example, some of the most progressive states (like California and Vermont) have at least considered adopting single payer healthcare systems only to have those plans stopped because of prohibitive costs.
Well, are those programs too expensive because healthcare simply can't be delivered more cheaply? No, they're too expensive, because they're trying to exist in the broader American economic model for healthcare. What if California was willing to fundamentally restructure its economy and reorder its healthcare system to force down costs like European countries have done? As a practical matter that would mean eliminating or at least severely undercutting private insurance and imposing very onerous restrictions on the private practice of medicine. They may even have to do enough of an economic reordering to warrant adopting their own currency to really take control. I could come up with all kinds of pretty explicit constitutional roadblocks to stop that. However, from a moral and self-determination standpoint, do I really have the right to say in perpetuity that they can never do this just because their ancestors joined the union in 1850? I think that's at least debatable.