Because if one truly loved one self, then one would be creating a world, a life, a set of experiences where all the sexual unions one engaged in would be recognized and experienced as the divine loving unions they are. To experience SAFE sex, one must be safe. In self, with others. The danger is failing to love yourself and each other while you're sexing. And herein lies the most difficult awareness and growth.
Many people think they know what love is, when they're only experiencing infatuation, or neediness.
And there's total freedom to be and to do. That-Is, you will truly see the divine in everyone and find that you are open to love everyone. There will be those who are not so open, who simply are not ready to receive the abundant love you have to offer. There will be those for whom you don't have strong affinity even though you love them. But mostly it's a matter of losing specialness.