Many people defend religion by claiming that morality is impossible without it. But humans have moral instincts, and even non-believers try to follow them - though not all to the same degree. Muslims recognize this innate good nature of people through a doctrine called ‘fitrah’.
Islam encourages moral reasoning, but also offers guidance on matters that are morally ambiguous. Take for instance the problem of abortion and its permissibility. Muslims believe that the soul is breathed into the body 120 days after conception, and this is when the fetus becomes human. Abortion before this point is generally allowed but not afterward, except in rare cases such as if the mother’s life is at risk.
This is not the only position that can be defended through reason, but it is the one that Muslims are expected to follow, while seeking transcendence - meaning that this decision is part of one’s relationship with God. The result is spiritual growth and the satisfaction that derives from a working relationship with God.
Another benefit of religious traditions is that they offer icons who integrate a system of morality into exemplary lives. Ethicists who attempt to start from a blank slate can have difficulty balancing and reconciling different imperatives in this way. For example, Peter Singer has been faulted for putting so much stress on the obligation to save lives selflessly that his prescriptions might not result in a life worth living.
We should be mindful of the critique of religion that it can detach from ethics and reason, becoming inhumane and superstitious. Some would use this as a reason to abandon religion altogether. But consider what is lost when moving from Islamic humanism to secular humanism. Or look at the people that have tried this already and see how they are faring, spiritually. Morality is possible without God, but some people want the morality that brings them to God.