We tried that. It didn't go well for any involved.

At the time only side wanted to leave. That's no longer the case.

Vast parts of the US are not economically viable and basically propped up by blue states.

Not a great line of argument. Vast parts of the US are not food secure and are "basically propped up by" a conservative bread basket. Large portions of the agricultural industry are not economically viable without illegal immigrants. Much of the defense industry and military is populated by conservatives. Such examples are as numerous as they are irrelevant to sensible discussions of policy.

It seems relevant to the chain of comments they were responding to. They are disagreeing with the comment that says multiple states might want to split up the country now, by pointing out that some of them might not be economically viable if they did.

You’ve come up with more reasons not to split up the country, by pointing out some ways the other parts of the country might have trouble.

I think (correct me if I’m wrong) you disagree with the partisan jab at the end, not the actual line of argument.

Fair enough. Indeed I object to the partisan framing but I suppose there is a valid point to be made about the generalized case here.

I wasn't thinking carefully enough because I've grown accustomed to such lines of argument being simultaneously partisan and irrelevant.

We’re better as one country, we just need a France or Germany sized organizational unit that can do interesting projects but is still small enough to be agile.