Only in the Catholic Church does one find the fullness of the Faith. Outside the Catholic Church there are certainly beautiful examples of grace at work. However, those graces all point and lead to the fullness of the Catholic Faith found in the Catholic Church. To enjoy the fullness of the Faith, one must be in communion with the Church that Jesus Himself founded, the Church to which He gave authority to act in His name.
Regrettably, most non-Catholic ecclesial communities have relaxed the teaching of Christ regarding divorce and remarriage, and teaching on artificial contraception varies in the non-Catholic eastern churches from the Catholic teaching to a permission to engage in the abomination of artificial contraception. If some had their way, the German Catholic bishops, for example, they would have the Catholic Church also relax Christ's teaching, if that were possible.
The Catholic Church alone preserves the teaching given her by Jesus Christ, i.e., that every valid marriage cannot be dissolved by man, and that artificial contraception is, indeed, an abomination, an affront to God. Non-Catholic churches that permit couples to enter into second "marriages" (while a first spouse is still alive) clearly contradict the teaching of Jesus Christ. The Catholic Church considers such "second unions" to be adulterous, as did Christ (Mt 5:31-32). Unless grounds for nullity exists, i.e., proof that a (previous) union was never valid, and therefore never existed (cf Annulment/Decree of Nullity), then a marriage is for life.
In brief, like it or not, the Roman Pontiff is only answerable to our Lord Jesus Christ. Popes can be reprimanded for their personal behaviour and clumsy personal comments, but if a teaching of faith and/or morals is defined ex cathedra, that teaching enjoys the protection of the Holy Spirit. Point of fact, no pope has ever taught heresy ex cathedra. While the eastern churches were mired in heresy for long periods, the Roman Church remained (and remains) orthodox. The eastern national churches, having demonstrated a history of error, are simply not in a position to challenge Roman authority in faith and morals.
Catholics, if they be Catholics, are the first to admit to the many wrongs committed in the name of the Church. Pope Saint John Paul II demonstrated contrition on behalf of all Catholics to remind us that we all bear the wrongs of the past and must seek forgiveness from God. However, those wrongs do not invalidate the claims of the Church to be the one True Church. Abusus non tollit usum; the abuse of a thing (by unfaithful Catholics) does not render it (the Church) invalid.
Despite what some might erroneously and irresponsibly claim, the Catholic Church has never taught error in faith and morals. Individual laymen, priests and bishops might fall into doctrinal heresy, but the Office of Peter enjoys the protection of the Holy Spirit. Christ promised to protect the Church under Peter (and his successors!). No other church can make that claim, and that is another reason why one should be Catholic.