Religious engagement and practices encourages and supports "clean living." Research has consistently found that religious people are less likely to engage in criminal behavior, marital infidelity, alcoholism, unprotected sexual activity as well as being more likely to engage in pro social behaviors such as volunteerism and charity. Thus, those who tend to report being spiritual, religious, or both tend to behave themselves pretty well. In a nutshell, people in the church choir usually don't rob banks. Check out Harold Koenig's Handbook of Religion and Health
as well as his Handbook of Religion and Mental Health
for excellent reviews if interested in the scholarly support for this.
Religion and spirituality encourages ethical behavior in their sacred scripture readings, in their models or exemplars for behavior (not only well known religious figures such as saints and founding members of religious traditions but also among religious elders, pastors, teachers, and congregants).
My point really is that overall, research supports the view that spiritual and religious practices (e.g., meditation, Church sponsored social justice ministries, religious service attendance) have certain physical, mental, community health, and ethical benefits.
Of course there are many examples of religious beliefs and practices being terribly harmful to self and others and of course there are many examples of outstanding non religious and completely secular organizations and individuals who are outstanding models for ethical behavior, community engagement, and physical and mental health. So, there are exception to these general principles for sure but the overall trend suggests that religion does assist and support people in living more ethically.
So, to answer the question, "do we need religion to be ethical?" The answer appears to be no but it could be helpful under the right circumstances.
What do you think?
Some comments on this post and elsewhere have asked for research evidence. I've listed some of this peer reviewed material below. The review articles and books might be the best place to start if you have limited time. Otherwise, consider doing a PubMed, PsycInfo, or Google Scholar search as well.
Bormann, J. E., Gifford, A. L., Shively, M., Smith, T. L., Redwine, L., Kelly, A., Becker, S., Gershwin, M., Bone, P., and Belding, W. (2006). Effects of spiritual mantram repetition on HIV outcomes: A randomized controlled trial. Journal of Behavioral Medicine, 29, 359-376.
Hackney, C. H., & Sanders, G. S. (2003). Religiosity and mental health: A meta-analysis of recent studies. Journal for the Scientific Study of Religion, 42, 43-55.
Hill, T. D., Ellison, C. G., Burdette, A. M., & Musick, M. A. (2007). Religious involvement in a healthy lifestyles: Evidence from the survey of Texas adults. Annals of Behavioral Medicine, 34, 217-222.
Kendler, K. S., Gardner, C. O., & Prescott, C. A. (1996). Religion, psychopathology, and substance use and abuse: A multi-measure, genetic-epidemiologic study. American Journal of Psychiatry, 154, 322-329.
Koenig, H. G., McCullough, M. E., & Larson, D. B. (2001). Handbook of religion and health. New York: Oxford.
Leigh, J., Bowen, S., & Marlatt, G. A. (2005). Spirituality, mindfulness, and substance abuse. Addictive behavior, 30, 1335-1341.
Marks, L. (2005). Religion and bio-psycho-social health: A review of and conceptual model. Journal of Religion and Health, 44, 173-186.
Marsden, P., Karagianni, E., & Morgan, J.F. (2007). Spirituality and clinical care in eating disorders: A qualitative study. International Journal of Eating Disorders, 40, 7-12.
Masters, K.S., Spielmans, G. I., & Goodson, J. T. (2006). Are there demonstrable effects of distant intercessory prayer? A meta-analytic review. Annals of Behavioral Medicine, 32, 337-342.
McClain, C., Rosenfeld, B., & Breitbart, W. (2003). Effect of spiritual well-being on end-of-life despair in terminally ill cancer patients. The Lancet, 361, 1603-1607.
McCullough, M. E., Hoyt, W. T., Larson, D. B., Koenig, H. G., & Thoresen, C. E. (2000). Religious involvement and mortality: A meta-analytic review. Health Psychology 19, 211-221.
Michalak, L., Trocki, K., & Bond, J. (2007). Religion and alcohol in the U.S. national Alcohol Survey: How important is religion for abstention and drinking? Drug and Alcohol Dependence, 87, 268-280.
Miller, L., Warner, V., Wickramaratne, P., & Weissman, M. (1997). Religiosity and depression: Ten-year follow-up of depressed mothers and offspring. Journal of the American Academy of Child and Adolescent Psychiatry, 36, 1416-1425.
Oman, D., Shapiro, S. L., Thoresen, C. E., Plante, T. G., & Flinders, T. (2008). Meditation lowers stress and supports forgiveness among college students: A randomized controlled trial. Journal of American College Health, 56, 569-578.
Pardini, D., Plante, T. G., Sherman, A., & Stump, J. E. (2000). Religious faith and spirituality in substance abuse recovery: Determining the mental health benefits. Journal of Substance Abuse Treatment, 19, 347-354.
Plante, T. G., & Sherman, A. S. (Eds.) (2001). Faith and health: Psychological perspectives. New York: Guilford.
Plante, T. G., & Thoresen, C. E. (Eds.) (2007). Spirit, science and health: How the spiritual mind fuels physical wellness. Westport, CT: Praeger/Greenwood.
Powell, L., Shahabi, L. & Thoresen, C. E. (2003). Religion and spirituality: Linkages to physical health. American Psychologist, 58, 36-52.
Seeman, T. E., Dubin, L. F., & Seeman, M. (2003). Religiosity/spirituality and health: A critical review of the evidence for biological pathways. American Psychologist, 58, 53-63.
Shreve-Neiger, A. K., & Edelstein, B. A. (2004). Religion and anxiety: A critical review of the literature. Clinical Psychology Review, 24, 379-397.
Siegrist, M. (1996). Church attendance, denomination, and suicide ideology. Journal of Social Psychology, 136, 559-566.
Stewart, C. (2001). The influence of spirituality on substance abuse of college students. Journal of Drug Education, 31, 343-51.
Worthington, E. L., Kurusu, T. A., McCullough, M. E., & Sandage, S. J. (1996). Empirical research on religion and psychotherapeutic processes and outcomes: A ten-year review and research prospectus. Psychological Bulletin, 119, 448-487.