She made her novel's villain a Northerner who moved South, Simon Legree, and made her Southern whites generally admirable, if weak and flawed, figures.
Of course, slaveowners bent on secession would take Stowe for a South-hater and a villain, but they'd say that about anybody who didn't whole-heartedly support slavery.
Anyone who said or wrote a critical word about slavery was assumed to be an enemy and a devil.
That in this, as in so many other things, you automatically take the slavers' side, is yet another reason why conversations with you tend not to be worth the time.