Given enough time, if the burning desire to naturally procreate (meaning heterosexual sex) was greatly reduced, the population would definitely die out.
Sex is one of our basic drives. Think about it.
Take away the basic drive to eat and drink (get rid of thirst and hunger), and the population would die out even more quickly.
To those who say it is wrong to say that homosexual sex is unnatural, I disagree. We're talking about nature here. What exactly is that stuff that comes out of a penis when a man ejaculated? Oh yeah... sperm. And what is The purpose of sperm? To give a another man an enema? :D Why exactly does sperm swim toward a female's eggs if it would rather swim up a man's colon? :)