HIV aside - because (I'm not getting into the controversy here) YES it does exist, however not for the common reasons the general public believes.
Why risk yourself to HERPES, CHLAMYDIA, WARTS, BACTERIA INFECTIONS, SYPHILIS?
Most of these can be easily treated, others are 'life long' or will take more concentrated effort from a natural standpoint to cure...whatever there is a risk with frivolous sex. Not to mention pregnancy, while it's not a disease it does have life long effects and can be a huge emotional stressor if not 'planned'.