The Catholic Church does not denounce all other Christians. In fact, the Catholic Church affirms that those who are validly baptized are incorporated into Christ and are therefore in a real, though imperfect, communion with the Catholic Church.
However, there are differences in doctrine and practice between the Catholic Church and other Christian denominations. The Catholic Church believes that it is the one, holy, catholic, and apostolic Church founded by Jesus Christ, and that it possesses the fullness of Christian truth. As a result, the Catholic Church may express concerns or disagreements with the teachings or practices of other Christian denominations when they differ from Catholic doctrine.
It is important to note that Catholics are called to treat all people with respect and charity, including those with whom they disagree. The Catholic Church encourages ecumenical dialogue and cooperation with other Christians in areas of common concern.