What you are really trying to say, that there was not enough interest in slave ownership or slave owner political power to get an amendment to the Massachusetts off the ground.
Do you believe in the right to bear arms? What if you lived in a state where this was an unpopular view of the majority of people, such as Massachusetts?
Whether or not a democratic majority approves of your right is irrelevant to whether or not it is a right.
A Judge ruling you don't have a right to own a gun doesn't make it true, and a majority of the population agreeing with this liberal judge also doesn't make it true.
It is either true or not on it's own merits, and no ruling by a judge, or public opinion result will change that. Truth is not subject to democratic or judicial whim. It either is or isn't, regardless of the opinions of Judges or citizens.
I think slavery is evil, but according to the laws of that era, it was legal, and i'm not going to pretend it wasn't just because that makes me feel better. I'm going to tell the truth on this point, and i'm going to call out people who are telling lies on the same point. (Meaning the Judges of Massachusetts in 1780.)