Situation B: Two men lead attacks on US Federal Government buildings in an attempt to spark a race war which they believed was divinely ordained, failed, and were subsequently executed. John Brown attacked the Federal Arsenal at Harper's Ferry, while Timothy McVeigh attacked the Federal Building in Oklahoma City. In both cases innocents were killed as a result of the attacks, and in both cases their actions hurt their cause in the public mind and encouraged the expansion of paramilitary police forces designed to prevent similar future strikes.

If this is a question of humanitarian ideals, you might expect that both would be repudiated for their actions; even if we hate slavery, surely a student of history should recognize that slave revolts tend to involve mass murder even when successful which means that regardless of the validity of their complaints, both were attempting to start a genocidal war. Of course, from the point of view of political expediency there is no conflict whatsoever; the neofascist terrorist is a threat and thus irredeemably evil while the radical abolitionist terrorist is a predecessor and thus an inspiring heroic figure.

One of those is a war to stop something which is actually bad. The other isn't. That's not a trivial distinction.