There is a significant difference between saying, "The Church is wrong about this issue," and doing something that the Church condemns, and acknowledging that it is sinful.
There was a time in my life when I got drunk a couple times a week. But I didn't justify it by saying that drunkenness is OK; I recognized that it was wrong, got my head straight, and stopped getting drunk.
Mr Biden, when he speaks out about abortion, expresses no sense whatsoever that abortion is seriously immoral/sinful. It is as though abortion is on the same level as having a nose job.
Imagine a Catholic politician saying, "I believe that abortion is seriously immoral and sinful. But the current state of the law and the Constitution in the United States is that it is permissible, so in my capacity as an elected official I will not do anything to impair the legal rights of my fellow citizens, even though I believe that in exercising those rights they are committing an immoral act."
But no Leftist will ever say this, because it violates the absolute highest moral imperative in Leftism: YOU MUST NEVER BE JUDGMENTAL! [Except against Christians].