Virginia didn't really come as close to abolishing slavery as many people think. A resolution saying that legislative action against slavery was "expedient"--without specifying any particular plan--was defeated 73-58. ("Only the East's extra legislative seats prevented nonslaveholder power from truly menacing the Slavepower. The legislative malapportionment of 1829 gave western Virginia seven less, eastern Virginia seven more delegates than a one-white-man, one-vote apportionment would have provided. A shift of seven votes would have narrowed a rather substantial 73-58 vote against the expediency of legislative termination [of slavery] into a razor-thin 66-65 defeat for nonslaveholders." William W. Freehling, *The Road to Disunion: Secessionists at Bay 1776-1854*, p. 188.)
But "without specifying any particular plan" is important here. The devil, as usual, was in the details. There were at least two very different plans. Thomas Jefferson Randolph introduced a proposal to free all slaves born after 1840 (when they became 18 in the case of women, 21 in the case of men) and then deport them to Africa, argued that there was no obligation to pay masters compensation, because no slaves *currently* held would be emancipated without their master's consent. (Indeed, under Randolph's proposal, no slave born in Virginia need *ever* be freed, since even slaves born after 1840 could be sold to the Deep South before their otherwise-emancipating birthdays...)
An alternate plan was proposed by William Henry Brodnax, whose scornful treatment of Randolph's proposal shows one of the crucial weaknesses of the emancipationists--their disagreements about how to accomplish emancipation. Brodnax thought that it was preposterous to combat impending dangers with a plan that would not even begin to go into effect for thirty years. "[W]hat is to become of...our safety...in the meantime[?]" Slaves would become impatient, and those born before 1840 would be angry that they would be held in perpetual bondage, while younger ones would be freed. Virginia legislatures would spend "winter after winter" debating whether to repeal the law, further inflaming passions. Moreover, "Randolph's proposal would give every gentleman 'the strongest temptation to convert himself into a negro-trader.' Owners could 'sell and pocket the value of every one of these post-nati, up to the very hour' of adulthood. Under 'this fanciful' emancipation, where not 'one single negro ever would be liberated,' blacks would rise like madmen when sold down river in the final hour. Randolph's chimera was thus a scheme of liberation destined to free no one, a preservation of domestic peace destined to produce 30 years of domestic warfare, a maturation of Virginia paternalism destined to make every patriarch a child-seller. "William Henry Brodnax proposed instead that deportation be commenced immediately, and emancipation soon. He would begin by exiling 6,000 free blacks a year, at state or federal expense. "Within ten years,' no free black would remain. After this 'process...shall have demonstrated the practicality...of gradual deportation,' Virginia should move on to deporting 10,000 slaves a year, with compensation to masters. 'In less than 80 years,' not one slave would blacken lily-white Virginia. Expensive? Certainly. But less costly and more moral than the alternative: slaughtering domestics during the next insurrection panic, a catastrophe Thomas Jefferson Randolph's proposal would hasten." Freehling, *The Road to Disunion: Secessionists at Bay 1776-1854*, p. 185.
So when you have two such different plans, you have to ask yourself: Even if emancipationists could squeeze out a bare majority for gradual emancipation "in principle," could any particular plan get a majority? Very likely any plan would be defeated by a coalition of anti-emancipationists and emancipationists who desired a different approach...