Their justification, and equally their motivation, is in our (Christian) disunity
I dont think so. I for instance am not motivated or justified by the division between Orthodox and Catholics. I personally was not confused about this when I was confronted to become a Christian. Again, accepting Jesus Christ as personal Lord and Savior was forefront, not which church to join.
Look, i really dont care if Catholicism is not the true church, I honestly dont care which church/denomination it is
Ok, but you certainly care about the Catholic trait of believing in one church at expense of others. Like wanting unity amongst mankind believing everyone should be one race, one color, be it black, or red, or white. Or like trying to figure out who was the real Jew when Jesus was born, so that their authority could unify others. But pick one, Essenes, Pharisees, Saduccees etc., otherwise who draws the line, who really represents Judaism to the world, even to itself?
They were all part of Judaism, just as surely as black, red, white and yellow are all part of human race.
Again we are at odds of just what unity in Christ and with each other simply is.