What was the argument of northern Whigs?

Northern Whigs argued that slavery was an immoral institution that had no place in a free and democratic society. They did not want slavery to be expanded into new territories and believed it should be banned altogether.

They pointed out the contradiction of a nation founded on the ideal of freedom while holding millions of people in bondage and also noted how slaveholders wielded disproportionate political influence due to the 3/5ths clause. Their ultimate goal was to abolish slavery entirely, but since there was opposition in the South, their initial actions centered on containing its propagation by opposing its existence where it did not then exist rather than its existence where it did already exist.