Webster called slavery a sin but denied the North any legal duty to act.

Evidence

In an 1837 letter he cautioned his daughter Eliza not to become too involved. … Eliza, slavery is a great sin and a great calamity—but it is not our sin, though it may prove to be a terrible calamity even to us in the north. But we cannot legally interfere with the south on this subject—and every step which the abolitionists take is tending to defeat their own object. To come to the north to preach and then disturb our peace, when we can legally do nothing to affect their object, is, in my view, highly criminal, & the preachers of abolitionism deserve the penitentiary. — Tamara Lanier, From These Roots, 216