Pax says, “If we pick and choose based upon our own wisdom, then the Assumption will be but one in a long list of things that people might discard.”
Irish_Catholic says, "Because it is dogma. All dogmatic definitions must be believed by Catholics. If you are a Catholic, then you will believe what the Catholic Church teaches. And the Catechism states:
CCC 82: As a result the Church, to whom the transmission and interpretation of Revelation is entrusted, “does not derive her certainty about all revealed truths from the holy Scriptures alone. Both Scripture and Tradition must be accepted and honored with equal sentiments of devotion and reverence.”
CCC 87 Mindful of Christ’s words to his apostles: “He who hears you, hears me”, the faithful receive with docility the teachings and directives that their pastors give them in different forms."
Such statements seem clear and wonderful and because they are so common-sensical they generate a feeling of security.
But in practice it doesn’t come out so neatly and cleanly.