In addition...based on the information available regarding STD's...it is also dangerous.
Given the dangers...you would be best advised (but certainly not required) to check out the information included in this presentation, whether you believe in the moral/spiritual side or not. Such behavior endangers yourself and those with whom you practice sex.
I do not believe this is an accident. In my faith, God in Heaven was certainly aware of all of this when He devised our lives and relationships as He did.
But, He has also given us all our free agency/free will and we are free to do as we please. Our actions however do not free us of the consequences associated with those actions. The consequences of rampant promiscuity are becoming more and more patently obvious in terms of their health impact.