Frank --
Compare Seward's language to that employed by William Wilberforce and others who campaigned against slavery in Great Britain. Wilberforce spoke against slavery without demonizing English slaveholders and their supporters.
John Brown enjoyed considerable support -- financial and otherwise -- from men like Seward who would not have minded if most Southerners (those of white European descent) ceased to exist on this continent. If this goal was beyond reach, destroying Southern economic and political power was an acceptable substitute.