One cannot take passages from the Declaration out of context. The part you quote does not negate the self evident truths, nor grievances that prompted the separation in the first place. Not to mention the reference to prudence, dictating that Governments long established should not be changed for light and transient causes. The compromise on the issue of slavery, that was necessary in order to get the Constitution ratified by all the states, was the seed that grew into the final conflict that completed the American Revolution. Sad, but true.