In the late 1840s, during the lead-up to the Compromise of 1850, some federal legislators argued that the prospective state of California should be divided in half and ultimately be admitted as two states. These were southerners, of course, who were proposing that the Missouri Compromise line be extended to the Pacific. The northern portion would be admitted as a free state; slavery would be permitted in the south.
It was not to be, because most northerners, and some southerners (including Louisiana slaveholder Zachary Taylor), objected, for a variety of reasons, and most of us would say that the good guys won that fight. But Lawprof Ilya Somin's recent post at Volokh makes me wonder: would we all not have been better off, at least in the long run, if proponents of the extension of the Missouri Compromise line had succeeded?