Death.

> It follows that many of those who died from AIDS would still be alive today had the Catholic Church abandoned its condom ban in the 1980s, as it became clear that condoms were (and still are) the most effective practical measure to prevent the spread of the disease.

http://en.wikipedia.org/wiki/Catholic_Church_and_HIV/AIDS

Also forbidding sane family planning and the prevention of unwanted offspring, where lack of necessary resources causes even more disease and more death.