Lincoln, alone, opposed secession for these reasons:
Lincoln would not allow secession, regardless. The South viewed Lincoln as purporting a strong centralized Federal government that favored Northern interests. Many Southern states, which viewed Lincoln as a despot, now believed their suspicions of Lincoln had been confirmed.
First Inaugural Address March 4, 1861
Secession is Unlawful
Secession Will Destroy Democracy
Indianapolis, Indiana February 11, 1861
Lincoln's Thoughts and Opinions
Lincoln may have thought the fifth point was the most important. If you traveled the earth in 1860, and visited every continent and every nation, you would have found many examples of monarchies, dictatorships, and other examples of authoritarian rule. But in the all the world, you would have found only one major democracy: The United States of America. Democracy had been attempted in one other nation in the eighteenth century - France. Unfortunately, that experiment in self-government deteriorated rapidly, as the citizens resorted more to the guillotine than to the ballot box. From the ashes of that experiment in self-government, rose a dictator who, after seizing control in France, attempted to conquer the continent of Europe.