The Lovers is one of the most complicated and obscure cards, as most Air cards are. The point I see is that, although I could drone on and on about alchemy and Qabalah and astrology (what little I know of it) although it could mean straighforward sex, that is but one of a a great myriad of larger significances. To eschew those, in my opinion, is to lose a huge amount of personal development connected to one of the most important cards. If I had to arrange them in order of importance it would be the Fool, Justice and the Lovers, in that order (all three, incidentally, Air cards).
A discussion between an occultist and an intuitive reader is doomed to failure, because personal interpretation can be used to justify anything, and can't be argued with.
Meta discussion aside, the idea of the Lovers is union through separation in one of its most abstract forms, and sex is but one way humans achieve that union, but there are many others, most far more mundane. However the Lovers is a card denoting the basic machinery of the universe in terms of anything that happens, happens as a result of two opposites annihilating each other.
Now, don't take me at face value, because the following will sound strange, but there is a point (I hope). If I am holding a pen, the Lovers would show I am "making love" to it, outpouring my own creative power, separations between me and the pen are destroyed (it becomes part of me) and together, we create something else, namely, writing. If I throw a ball, I am outpouring my "love" to it (creative force) and something new is created, inertia. The most basic spiritual mechanics of having sex and throwing a ball are exactly the same, as anything that happens is an act of Love. So, to say it is about sex is true, provided you're talking about having constant sex every second of your life with the entire universe. That, contracted into the mundane, in a reading could mean sex, but not just that.
Even the story of the apple illustrates this, but that's for another thread, which I would be happy is someone were to start.