That's a worthless argument...
The Bible itself tells when Jesus says... "I am the way, the Truth and the life, nobody comes to the Father accept thru the Son"... so... if "they" are seeking God thru any other way...(Mary, Saints, Rituals, Icons, Priests, Pope's , dead corpses and body parts, what ever) "they" are not practicing Christianity but something else. Tacking on Christ;s name does not make it acceptable nor Christian. Jesus again teaches that He is the only "intersession"...which takes you back to square one #1.... ..."who are "they" following"... Scripture or the teaching of the church of it's leadership? Like all false religions catholicism follows their pattern...
The Catholic Church put the Bible together. It existed before the Bible. Jesus wrote nothing except on the sand which disappeared. He believed in teaching through people, strong or weak. Those people created the Catholic Church to exist until the end of time. That's what Jesus wanted.