There is only one criterion for weighing our actions: Do they serve indwelling life or don't they? If they serve the world of form only, they serve what is unreal. On the other hand, if actions serve to evolve awareness, then they are aligned with the purpose of indwelling life.
The degree to which sexual acts enhance the indwelling life of participants depends on the consciousness that initiates them. To be conscious is to see the big picture. Conscious beings consider carefully the effects of any act on others. They know that any choice they make must benefit all equally in the evolution of awareness.
Many sexual "spiritual" practices are designed to enhance energy, which in turn increases consciousness but not always equally to both participants. Using another to enhance primarily one's own energy can provide short-term energy boosts but will ultimately deplete not only oneself, but also one's environment. A practice that focuses on self-gain is selfcentered, a condition that de-spirals the DNA strand and warps the web of existence, creating karmic repercussions.