If the Catholic Church is in fact the one church of Matthew 16 established by God circa AD 33, on Pentecost, in Jerusalem, to which the apostles and their successors belonged e.g. Ignatius of Antioch etc.,then why would anyone not want to belong to this church?
Stipulation: If you do not believe that Jesus established the Catholic Church, and can prove it (e.g. provide the name of the person who founded the Catholic Church and when) then I would certainly understand. Just looking for specific reasons (in light of the knowledge that the Catholic Church was founded by God).