It probably would have been a good idea to actually prepare a social and political framework for eliminating slavery.
One that did not involve the senseless slaughter of some 600,000 of the best Americans, mass atrocities that set the bar for coming wars, the dismantling of the constitution, the political and cultural shattering of the American body politic.
Worst of all perhaps, the loosing of some hundreds of thousands of people from the bonds of the only social order they knew, with nothing whatsoever in its place; people without literacy, property, without even the most basic cultural forms like the nuclear family or basic concept of political organization.
Loosed into an occupied war zone and then left to fend for themselves without any economic resources or social capital in a state of de facto slavery, without even the security afforded by actual slavery, or the salutary benefit of close interaction with religion, literacy, education, manners, law, marriage, etc., necessary for success in a free society and complex market order.
Because of that madness, fueled by moral fervor untempered by reasoned forethought, allied with political opportunism, today, 150 years later, we have a huge underclass of blacks whose condition in life is more morally degraded than even that experienced on the plantation; a black middleclass dependent nearly completely on the federal and state civil service subsidy, and affirmative action; a lower class living in barely civilized conditions, likewise dependent on a faceless master.
Housing projects where elevators serve as public bathrooms. Addiction and vice rampant and unchecked. Schools that are poorly disguised factories for the prison system. Gangs rule the neighborhoods and operate as press gangs for fresh blood in the prisons through which some half of black youth circulate at one time or another.
Marriage is hardly known, commerce and business totally absent and impossible, and a police presence akin to what would be needed in an occupied war zone.
Add on top of all of this a powder keg of barely suppressed hatred and resentment ready to explode at any time, and stoked regularly by classes of political opportunists from within and without the black community. Anger and alienation that will spill over into violence the moment the demographics shift sufficiently in a specific locale, and has done so like clockwork, one city and neighborhood after another in a spreading wave of urban ruins.
Before you respond with pretended moral outrage, look around your neighborhood and tell me where you choose to live; anyone who can afford to runs the other way, and every year the problems grow greater and less amenable to constructive remedy. You can turn your head the other way, feign moral outrage, or blame some scapegoat like the drug war or the "Democrats." That is convenient and also not reality.
What you're looking at, if you choose to do so, is the obvious outcome of one of history's most reckless moral crusades to rip apart social institutions without deigning to set one stone upon another in the construction of some social edifice to replace it or to even make an attempt at sane transition.
Your argument is all the weaker when you consider the greater power of the moral imperative to end slavery, than that of tearing down a state that today is at least in pretense sanctioned by popular ballot, free speech, and freedom of the press, etc.
So yes, the moral opponents of slavery SHOULD have considered practical realities, real world conditions, likely outcomes, and heard sober voices and arguments about the proper course to take to end the blight of slavery. Unfortunately, that did not happen.
Don't think that playing the rhetorically powerful slavery card will make me shy away from controversial facts. I will still have the better hand.