The short answer is: Catholics are happier than non-Catholics. He is my son. I want him to be happy. What choices does he have?
He could be a Baptist. Baptists are happier than Materialists. Baptists and Catholics have differences. I'm a Catholic but you are never going to find me attacking Baptists. We say the same Creed. A cigarette-paper between me and most Baptists.
Catholics are, for the most part, secure in their world view – and I don't mean complacent. Yes, there is an element of Faith; but Faith is not, as Dawkins alleges, prized for being blind, for flying in the face of Reason. This, in spite of centuries of Catholic thinkers whose commitment to Reason is rock-solid. He is impertinent to tell us what we believe. It is not unreasonable to have Faith in God, any more than it is unreasonable to believe that there are moral absolutes. We cannot see God; but nor has anyone ever seen a moral absolute.
[Gerard Casey, may his sins be forgiven, has published a short piece on the web: Faith in Search of Understanding. It's great.]
The debate goes on, with clever people on either side. But the Faith-Heads, as Dawkins contemptuously calls us, have the better arguments. He famously refuses to debate William Lane Craig – perhaps because he has seen the video of Peter Atkins' mauling by Craig.
I suppose that Marxists are secure in their world view. But they really don't have any arguments left. The predictions of Marxism have demonstrably failed. Their social/political/economic experiments have failed catastrophically. The death-toll is vast. If ever a system of belief could be called blind, Marxism is egregiously the blindest.
Marxists are Historicists. They believe that the organisation of society should be in conformity with what Marx declared was the direction of History. Catholics believe that by trying to live in conformity with God's will they glorify God and serve their fellow men. It is centuries since any Catholics have attempted to use force to impose "God's will" on other people – and, in so far as it has happened in the past – it was deplorable. But people who believe in and understand Original Sin and who are enjoined by their Faith to emulate Christ (however feebly) are bound to produce a better society than those who are baptised by History.
Muslims (sometimes) say that there should be no compulsion in religion – Amen.
Sam should be a Catholic because it makes sense; it makes you happier; it makes you a better person. And the more people who are striving to live by Catholic teaching, the better the world will be.
Why isn't everyone a Catholic? In only a tiny minority of cases are non-Catholics people who have earnestly examined the issues and found themselves intellectually compelled to reject Catholicism. Far more common are those who, because of their upbringing and education in a secular society, just kinda assume that Christianity has had its day and is unsuited to today's more "rational" world. The most resounding success of Materialism is the wide-spread, but baseless, myth that some time in the last hundred-years-or-so there was a mighty battle between Christianity and Science – and that Science won. Clever of the Dialectical Materialists to have pulled that one off during the century when so much of their energy was invested in killing millions-upon-millions of people! You might have thought that the gulags and the killing-fields and the famines and the immiseration of whole societies would have dented their credibility just a bit.
In so far as National Socialism and International Socialism have done Nazi "Science" and Marxist-Leninist "Science", they have produced 100 Scientists against Einstein and the sick joke that was Lysenko.