if you draw a line across any country, you sign up for generations of violence until that line disappears

India?
In this case, the unionist population of Ulster made it quite clear that they would go to war if the line was NOT drawn.

Three counties were originally proposed, then hastily dropped when it was calculated that they would provide a Catholic majority - it was a deliberate and stated policy to create a Protestant state.

The policy was to place as many people as possible on the side they would choose.
What is your objection?

The creation of a sectarian state
The creation of two sectarian states, if that is defined as a state with a religious majority.