The longer quote is this:
"...it (an action the speaker disagreed with) forces so many really good men amongst ourselves into an open war with the very fundamental principles of civil liberty -- criticizing the Declaration of Independence, and insisting that there is no right principle of action but self-interest."
I love so many things about this Republican, not least of which is his respect for voters in that he makes fairly complex arguments of principle and expects the average American citizen to understand them. Respect for the intelligence of voters somehow seems quaint today, but one would think - or at least hope - that modern voters are not less intelligent and thoughtful than people were a hundred and fifty years ago.
The speaker, of course, is Abraham Lincoln. The action he was referring to was the Missouri Compromise, which explicitly expressed indifference to the rightness or wrongness of slavery.