the abolitionist movement in the main did not possess the political power in the american congress during the lincoln presidency to force the north into armed conflict with the south on principle. abolitionist leaders in the congress like charles sumner were *reactive* as opposed to proactive with regard to militia actions in the western territories.
preservation of the union was the primary official motive of getting into war. but already guerrila fighting had begun precisely over the matter of slavery in the western territories.
john brown was the spearhead of the militant abolitionists, but he had great problems influencing the rest. in brown's thinking, a war was inevitable and he was bent on escalating the conflict, on the terms of equality under god, a far more radical position than that officilly stated (early or late) on emancipation.
so if you would like to believe that *the* moral motivation for the federalists was the negro question, then you would have to show john brown as the leader of that movement. clearly, brown had no federal sponsors.
i think the crux of this question can be answered by evaluating the positions in the congress of the matters of the two revolutionaries most militantly opposed to the general oppression of the african. and those two are nat turner and john brown. in the end i think you will find that the north was NOT escalating the wars started by those two, but fighting their own war for separate purposes.
lincoln defended the principle of human rights for the african, but that fell far short of civil rights. one could argue that some segment of the african population in the south enjoyed human rights prior to the war. it's rather like newt gingrich attacking bill clinton on the question of marital fidelity.