An old eastern legend tells the story of a stranger who sought shelter for the night in another's tent. He awoke in the middle of the night and blasphemed God because he could not fall back to sleep. Awakened by the stranger's profanity, the scandalized tent owner drove the man from his home. In the morning, an angel appeared to the owner, exclaiming: "I sent a stranger to you for shelter. Where is he?" "I would not let him stay," explained the owner, "because he blasphemed God." "For forty years," replied the Angel, "God has been patient with that man. For one single night could you not bear with him?"
We are called to deal with unstable and volatile persons. Jesus himself did. Think of the scene when our Lord dined with tax collectors and sinners at Matthew's house (cf. Mk 2:13-17). These non-practicing individuals most likely did not go to synagogue. They did not live morally upright lives. I am sure they even swore and blasphemed during the dinner conversation. Jesus did not mind.
A non-practicing individual, be it a Jew 2,000 years ago or a Catholic today has a sort of instability about them. They change, seek, adopt something new, come back to something old. They sin and perhaps even act crudely. They are not on a stable foundation that a practicing person has. For the more a Catholic places himself before the sacraments, particularly the Eucharist, the more the grace of Christ can wash over him and literally convert him to goodness.
But that does not mean the volatile and unstable person is bad. And he is certainly not undesirable to God. Tax collectors and sinners have a purpose, and perhaps without them there would be no chance for people to exercise patience and become saints.