“It simply permitted it if the state wanted it.”
Which is what applied to Nebraska and Kansas too, didn’t it. Popular Sovereignty.
Except that wasn’t the agreement reached in the Missouri Compromise. It specifically said that slavery was prohibited north of the line. No “popular sovereignty,” just banned in the same way the Northwest Ordinance had banned slavery in the Northwest Territories in 1787. The problem came when the south realized that there were going to be more states joining the union north of the line than south of the line and wanted to renege. Stephen Douglas pushed the “popular sovereignty” idea in Kansas as a way to finesse a slave state into the union, preserving the south’s eroding power.