I have always thought that "The Wanderer" was a tad harsh when it comes to things like this.
I was raised Catholic and got married outside the Church. (in COURT, no less!) It would be a heck of a thing if my family refused to associate with me.
It also makes me think about 'closet sinners'. There are plenty of people in a state of mortal sin and an outsider cannot KNOW this by simply looking at said person.
So...if you can keep your sins under wraps you don't get ostracized from the family?
(Sorry if this offends anyone, but I grew up with more people like this than I care to recall. They always seemed to want to put on a big show about what great Catholics they were and how horrible everyone else was. Ugh. It gets tiresome after a while)
The whole point of this exercise is not to try to determine who is or is not in a state of grace.
The purpose is to ostracize people living in a habitual state of public sin who are flaunting the morals of the Church and society and expecting everyone to approve of their behavior and act like nothing wrong is going on.
It is not an attack on sinners. It is an attempt to eradicate approval of people living in a state of habitual sin.