Does anyone know an online copy, probably via Google, etc., of any textbooks on American Law printed circa 1850 or earlier? That would be a better determinate of what the thought of the time would be.
David, from what I've seen about the secession crisis of 1849-1851 there was never a consensus. But if you were to look at the talk of secession that arose during the War of 1812 (Hartford Convention) and the Nullification Crisis, the nation as a whole had a very dismal view of secession.
After the Mexican-American War there was a strong wave of nationalist patriotism. The secession crisis that arose caught many be surprise, but by and large everyone but the nascent fire-breather movement agreed that secession represented a failure of America's great experiment in republicanism. Following the Compromise of 1850 the there was a brief respite that only lasted until the Kansas-Nebraska Act of 1854. Remember though that from 1854 all the way till 1860 the South won nearly all of the political confrontations. Even so there was very little talk of secession in the North. This seemed to be because of three primary reasons; economic growth and western settlement diverted Northern attention, a true sense of nationalism that elevated the idea of Union to a higher cause had arisen, and the realization due to demographic changes that the North would eventually overtake the South so as to control the national government.
As others have said directly or indirectly allowing secession was untenable. To be effective as a way of addressing grievances (either real or perceived) states need the power, as supposedly sovereign entities, to unilaterally secede. Yet this totally undermines the very idea of a national government and creates a situation no better than the Articles of Confederation. On the other hand if secession is allowed only with the permission of the other states in a manner similar to the amendment process than each state remains at the mercy of the majority and still lacks sovereignty. The Founders and generations after found it easier to ignore the situation.
When one looks at the Civil War preservation of the Union was the primary reason that the average Northern soldier fought (this is not to be mistaken for the cause of the war which was beyond a doubt, slavery). Very few men from Northern states fought for the CSA while thousands upon thousands of Southerners fought in the Union armies. Outside of the primary cotton and tobacco regions the people were very divided over secession. The idea of "perpetual union" remained a very strong concept even within the minds of those living in the seceding states.
Benjamin