Agreed, Northerners were "guilty" of putting their love of country before their abhorrence of slavery.
They had already fought one terribly destructive war against Britain and were not willing to fight another, just as destructive, with each other over slavery.
In today's terms, they "kicked the can" down to future generations.
Considering that Civil War was roughly equivalent to the Revolution in percentages, I can't say that I blame them.
More like they pragmatically did what they thought was necessary to present a stronger front against the possibility of England changing it's mind about their secession.
But you dress up their motives very prettily.
They had already fought one terribly destructive war against Britain and were not willing to fight another, just as destructive, with each other over slavery.
Especially since most of the states in 1787 were still slave states. The "free" states would have been greatly outnumbered.