I suspect that many or most who deplore the Compromise of 1850 assume that it wasn't necessary - the South would have rolled over anyway. It's impossible, of course, to prove (or disprove) the consequences of contingent scenarios that never came to be. But the angry words of Alexander H. Stephens certainly suggest that, had the compromise failed, and had shooting broken out between Texas and the United States over the Texas-New Mexico border in late 1850 or 1851, the Civil War would likely have started out ten years early.
After the Compromise was brokered, Stephens became its champion. He helped lead the campaign in support of the Compromise in his native Georgia, decisively rallying public opinion behind the Compromise and away from secession in late 1850 and 1851.
But at the beginning of July 1950, Stephens was both angry and frantic. Having heard that President Zachary Taylor supported the immediate admission of New Mexico as a state, Stephens then received news that the president and his cabinet "had supported using the army if necessary to oppose Texas forces in New Mexico." On July 3, 1850, Stephens, already "smoldering", read an editorial in the National Intelligencer that appeared to confirm the report: the Whiggish newspaper urged that "If Texas advanced on Santa Fe . . . it would be the 'duty' of the army to defend it."
Stephens promptly sat down and wrote to the paper a reply (published by the Intelligencer on July 4)that both expressed his fear that this course would lead to general civil war and made clear that even moderates like Stephens would regard war as justified. Thomas E. Schott summarizes Stephens's letter in Alexander H. Stephens of Georgia: A Biography (from which the other quotes in this post are likewise taken):
Convinced beyond doubt that Taylor would use force to carry out his policy, Stephens sat down at his desk in the House and wrote a blistering reply to the editors. "The first Federal gun that shall be fired against the people of Texas, without the authority of law, will be the signal for the freemen from Delaware to to the Rio Grande to rally to the rescue." Whatever doubts there might be about the Texas boundary, "nothing can be clearer than that it is not a question to be decided by the army." In case of conflict, the Texas cause would be the cause of the entire south.
Here's a thought exercise. Imagine you're a northern politician in mid-1850. You detest the Slave Power, slavery and the proposed Fugitive Slave Act in particular. Do you hold your nose and support the proposed compromise because you fear civil war? Or, if you decide to oppose the compromise, do you do so because (a) you're confident the South will cave, or (b) war or no war, it's about time someone stood up to these people?
About the illustration, entitled Congressional Scales, A True Balance (1850):
A satire on President Zachary Taylor's attempts to balance Southern and Northern interests on the question of slavery in 1850. Taylor stands atop a pair of scales, with a weight in each hand; the weight on the left reads "Wilmot Proviso" and the one on the right "Southern Rights." Below, the scales are evenly balanced, with several members of Congress, including Henry Clay in the tray on the left, and others, among them Lewis Cass and John Calhoun, on the right. Taylor says, "Who said I would not make a "NO PARTY" President? I defy you to show any party action here." One legislator on the left sings, "How much do you weigh? Eight dollars a day. Whack fol de rol!" Another states, "My patience is as inexhaustible as the public treasury." A congressman on the right says, "We can wait as long as they can." On the ground, at right, John Bull observes, "That's like what we calls in old Hingland, a glass of 'alf and 'alf."