Actually only those are to be included as members of the Church who have been baptized and profess the true faith, and who have not been so unfortunate as to separate themselves from the unity of the Body, or been excluded by legitimate authority for grave faults committed.  Paragraph 22 Mystici Corporis Christi

in Pargraph 23: For not every sin, however grace it may be, is such as of its own nature to sever a man from the Body of the Church, as does schism or heresy or apostasy.