The point is that in this discussion this is a straw man. I could just as easily counter that Jesus said, as described in Matthew 18:15-17
"If your brother sins (against you), go and tell him his fault between you and him alone. If he listens to you, you have won over your brother.
If he does not listen, take one or two others along with you, so that 'every fact may be established on the testimony of two or three witnesses.'
If he refuses to listen to them, tell the church.
If he refuses to listen even to the church, then treat him as you would a Gentile or a tax collector."
The inference of this passage is that Christians are expected to live apart. In 1 Corinthians 5:10-12 Paul writes:
I wrote you in my letter not to associate with immoral people, not at all referring to the immoral of this world or the greedy and robbers or idolaters; for you would then have to leave the world.
But I now write to you not to associate with anyone named a brother, if he is immoral, greedy, an idolater, a slanderer, a drunkard, or a robber, not even to eat with such a person.
For why should I be judging outsiders? Is it not your business to judge those within?
As can be seen by Paul there is an assumption that there is a group of people who are within the Church and a group who are without. He assumes that our relationship to our brothers and sisters within the Church will be different than our relationship to those without.
As Christians it is our duty to Evangelize, that is to preach Christ to the world. We cannot do that if we don't know who we are. In a culture based on principles so apart from the principles of the Gospel it is almost impossible to be part of both worlds.
In 2009, in the wake of President Obama's ill conceived invitation to Notre Dame Jody Bottoms wrote impassioned essays on abortion and Catholic culture. Rod Dreher's response was to ask "What Catholic culture?" pointing out that a majority of "Catholics" in the United States help vote in the most pro-abortion president this country has ever had.
This is more a proof of why maintaining a Catholic culture is important that an indictment that it isn't.
It is incumbent on parents to instill Catholic culture on their children. They are the first teachers of their children. Unfortunately too many of them are themselves ignorant of authentic Catholic culture. So it fall to the catechist to introduce aspects of Catholic culture to their students, both child and adult.
For much of modern history the assumption has been that the catechist deals primarily with the child, the exception being those who are involved in RCIA. With an almost entire generation who have not been inculturated with the facts and Truths of Catholic culture it has fallen to the Church and its catechists to now look beyond their traditional students to the greater Church.
To stand against the modern culture of death we must be like the early Christians, who stood against the ancient culture of death that was the Roman Empire. We must, in some sense be apart. We must know who we are in order to stand in the modern marketplace of ideas.
In Isaiah God promises:
I will place the key of the House of David on his shoulder; when he opens, no one shall shut, when he shuts, no one shall open.I will fix him like a peg in a sure spot, to be a place of honor for his family;
This passage is referring to the king's steward. In the Church that is Peter, for, as St. Jerome said:
Where is Peter there is the Church.
So guided by Peter, and the Magisterium of the Church, we must stand against the culture a peg in a sure spot. Catholic culture is our peg.