Tell them the church is a hospital for sinners, not a showcase for saints. The transformation that begins at our Baptism is, for most of us, an affair of one step forward, three steps sideways, two steps back, and two steps forward. The human condition is characterized by original sin, the truth that things are not as they should be. The good news is that God comes to save us from the sinfulness of our lives and times.
Also, challenge those who will eschew the church because of the hypocrisy of some members. Sure there are some hypocrites, but what about the millions of Catholics of good character who authentically integrate the practice of the faith into their lives of love and service? Do other institutions (education, media, politics, etc.) exhibit an extraordinarily lower rate of hypocrisy than the church?
Hypocrites in the church do not negate all the good the church does. It’s the same with other institutions. There are some hypocrites in politics but we still vote. There are a few corrupt cops, but we still call 911. There are some doctors found guilty of malpractice, but we still go to the hospital.
Before making the judgment of hypocrisy, remember that Jesus commanded us: “Do not judge so that you may not be judged. For with the judgment you make you will be judged, and the measure you give will be the measure you get. Why do you see the speck in your neighbor’s eye, but do not notice the log in your own eye?” (Matt 7:1-3)