The pope has said condoms can be used to help stop the spread of aids in some circumstances. I wouldn't really classify homosexual marriage as "science" but the catholic prohibition on it deals more with natural law and sex having to have both the dual purposes of procreation and the loving aspect as well. We're quickly wading into the philosophical belief side of things. My entire point was essentially that while some catholic beliefs may conflict with what you believe they don't reject scientific evidence out of hand like people seemed to be suggesting.