Religion suppresses critical thinking.
The objection, in full
Religion teaches you to defer to authority — Scripture, tradition, the magisterium — rather than to think for yourself. It rewards belief and punishes doubt. The catechism is a list of conclusions to be memorized, not arguments to be tested. A worldview that demands submission of the intellect is incompatible with the intellectual maturity that defines an adult.
Dare to know! Have courage to use your own reason — that is the motto of enlightenment.
or, in plain terms —Religion teaches you to obey instead of to think.
Faith and reason are the two wings on which the human spirit rises.
The Catholic Church, far from condemning the use of reason, holds that faith and reason are mutually reinforcing rather than opposed. Though faith is above reason, there can never be any real disagreement between faith and reason, since it is the same God who reveals the mysteries and infuses faith, and who has endowed the human mind with the light of reason. The same God is the source of both, and the genuine conclusions of either, properly arrived at, cannot contradict the genuine conclusions of the other.
The Church therefore not only permits but requires the rigorous exercise of reason in the examination of the faith. The motives of credibility — the rational grounds for taking the Christian claim seriously — are the proper object of philosophical investigation. The compatibility of revealed doctrine with what is known by science, history, and philosophy is to be defended, where it is genuine, and where apparent contradictions arise, both sides are to be examined honestly. Methodical research in all branches of knowledge, provided it is carried out in a truly scientific manner and does not override moral laws, can never conflict with the faith, because the things of the world and the things of faith derive from the same God.
The image of religion as the suppressor of inquiry is a polemical fiction, contradicted by the historical record of Catholic universities, Catholic scientists, Catholic philosophers, and the Church's own magisterial teaching on the autonomy and dignity of the natural sciences. The objection survives only by ignoring what the Church actually teaches in favor of a caricature it would be easier to refute.