It all depends on what you believe in, what moral codes you adhere to. Christianity, for one, condemns it thoruoghly. It is not just about the fact that you could get infected with a virus, or something, it is just against God's will, as stated in the bible. And these days, health-workers recommend abstinence as a way of avoiding the dreaded HIV/AIDS.
I guess you just have to consider all the factors involved, and make up your mind what you want. Ultimately, the choice is yours.