Well not really. You do want to bias for dissolving a union.
If half the population is against it, it doesn’t matter if it’s 51% or 49%, it’s unpopular enough that it is tearing your nation in two.
Imagine the US civil war came down to a vote: “Sorry, 50.1% are in favor of slavery so we’re just going to keep practicing it in all of America”. Would the 49.9% be happy to live within that union? How about vice versa? The division is too deep.
If each 50% happens to be more or less perfectly geographically distributed, sure, but if not then you've just recreated the same problem twice (now something approaching 50% of each new division wants to immediately undo what you've just done).
If half the population is against it, it doesn’t matter if it’s 51% or 49%, it’s unpopular enough that it is tearing your nation in two.
Imagine the US civil war came down to a vote: “Sorry, 50.1% are in favor of slavery so we’re just going to keep practicing it in all of America”. Would the 49.9% be happy to live within that union? How about vice versa? The division is too deep.