As it was, Southern planters tried hard to institute means of control over their labor force that came close to reestablishing slavery. I think we can understand, why, from their point of view they wanted to, or felt they had to do that. Just don't think that you can make them look better than those who actually did get rid of slavery and not have people argue with you.
If it is in fact true that no slave ever arrived under the Confederate flag, that may have something to do with the fact that the CSA was under blockade throughout its history, and had few merchant ships to spare on unnecessary operations. As for illegal slave traders, really, how large a portion of the Northern population were they? Certainly far more Southerners would have been connected with the illegal importation of slaves -- taking delivery, keeping the slaves in bondage, selling, buying and transporting slaves -- than Northerners were.
I suppose we can take some comfort in the success of many American Blacks, but the price of that shouldn't be ignoring their case against slavery or making slavery into a particularly benign institution. It wasn't simply a question of participating in slavery and the slave trade or letting slaves rot. The hated "do gooder" spirit of Britons and Americans did a lot to break up the slave trade.
And Maryland? These Border States are bleeding under Lincoln's "oppression" until you need them to make a point, in which case they become "Northern" States. If you want to argue that Marylanders were Southerners held in the union by force, it won't do to attack them for "Northern hypocrisy." But it might get us further to consider Maryland a slave state that had made the right choice, for union and in time, for emancipation.