Why is so hard for some of my fellow Catholics to grasp this simple fact?

Cardinal Burke: "I can't imagine that any Catholic wouldn't know that abortion is a grievous sin, but if they don't, once they’ve been told, then they either have to cease to support abortion or accept the fact they are not a Catholic in good standing and pic.twitter.com/cHC1bSRVIU

— unborn lives matter (@RockofLifeNI) December 7, 2021