Stu, no matter what we USE sexual intercourse FOR, nature gave us reproductive organs to ensure the survival of the species by reproduction.
Nature made sexual intercourse pleasurable, not so it could be used to sell perfume, mens mags, or fast cars, but to ensure that we reproduce as often as possible

Even if you view sexual intercourse as simply a vehicle for sexual pleasure, the norm is still heterosexuality and a huge majority of humans are repulsed by any same sex behaviour.

The definition is "deviation from the norm".

I repeat what Keith said,...."so anything is permissible so long as we do it?"