Imagine testing circumcision on a really grand scale. Take a country with a population in the hundreds of millions. Manage to circumcise the majority of males. Then introduce AIDS.

That test has been done. The country was the USA in the 1980s. 

Test result: The USA now has one of the highest rates of HIV in the West, higher than most Western countries where the men have intact genitals.

The men of the USA were not protected by cutting their genitals. Imagine how much worse it could be today if American men thought they were protected.

So the next time you hear someone trying to convince you that circumcision is a great idea, remember: That test has already been done.