Yes they can...But they may not...
A Christian is a disciple of Jesus Christ...To say that someone became a disciple of Jesus Christ because he got baptized in water is a stretch...To become a Christian one must make a personal decision to become a disciple of Jesus Christ...
Jesus died so that we could be reckoned sinless...Without which we individually can not inherit the Spiritual Kingdom of God...
Have you ever actually attended a Catholic baptism? You make it sound like all that happens is that someone gets wet.
There's a bit more to it than that. Here's a taste:
Minister*: Do you reject sin, so as to live in the freedom of God's children?
[The ordinary minister of the sacrament of baptism is a deacon, priest, or bishop.]
Catechumen: I do.
M.: Do you reject the glamor of evil, and refuse to be mastered by sin?
C.: I do.
M.: Do you reject Satan, father of sin and prince of darkness?
C.: I do.
M.: Do you believe in God, the Father almighty, creator of heaven and earth?
C: I do.
M.: Do you believe in Jesus Christ, his only Son, our Lord, who was born of the Virgin Mary, was crucified, died, and was buried, rose from the dead, and is now seated at the right hand of the Father?
C.: I do.
M.: Do you believe in the Holy Spirit, the Holy Catholic Church, the communion of saints, the forgiveness of sins, the resurrection of the body, and life everlasting?
C.: I do.
M.: God the Father of our Lord Jesus Christ has given us a new birth by water and the Holy Spirit, and forgiven our sins. May God also keep us faithful to our Lord Jesus Christ for ever and ever.
Amen.
Sounds like a "personal decision" to be a disciple of Christ to me. If someone is going to stand up in front of people and publicly profess a lie, that's too bad, but it's not the church's fault. We're pretty clear on what's expected, and it's a whole lot more than just getting wet.