The first thing any Catholic must do to join another Religion is to lose his Faith.
After that it’s easy.
Most people that quit the Catholic Church do so mainly because of issues below the belt.
A conversion does not mean a loss of faith and it is unfair to dismiss it as such. It means a decision has been made that you no longer believe the Catholic church has the fullness of truth and that she is in error in certain doctrines. It does not mean you no longer have faith in the basic tenats of Christianity.
I love my Church but if someone is hindered from serving God with their whole beings should they remain then I wish themn godspeed to another worship home.