Isn't one Christian religion as good as another?
Such a notion is offensive to scripture, history, and reason. This idea is a heresy, called indifferentism by the Church.
History proves beyond question, as non-Catholic Christian scholars and historians will agree, that no Christian religion except the Roman Catholic Church existed prior to 1517. In the light of history, all other Christian religions are mere johnny-come-latelies.
The Bible tells us that Jesus founded one Church (Matthew 16:18), that He gave it one visible head (Matthew 16:19), that we are to obey the Church and its visible head (Luke 10:16) or perish eternally in the alternative (Mark 16:16). It is crystal clear in the Bible that Jesus did not found many churches. And since He founded only one Church, and expects us to obey it (Luke 10:16), we are bound to belong to it and it alone. Scripture, history, patristics, and reason tell us that the one Church Jesus founded is the Catholic Church.
Of course, this discounts invincible ignorance. Belonging to the one, true Church Jesus founded and our obligation to belong to it applies only if we know Jesus founded one Church and expects us to belong to it.