What do we mean by "sexual misconduct?" Here we are referring specifically to behaviour that harms the person who performs the act, or the other party - not all sexual conduct. Sex is prohibited to those who choose to be celibate e.g. monks or nuns. These persons have voluntarily chosen to abstain from sex to better concentrate on their spiritual progress. In a sexual relationship, if the two parties are consenting adults, not under-aged, not “attached” (legally or otherwise) to someone else, there is no harm done.

In Buddhism, we do not consider any action "sinful" in the sense that we transgress a divine commandment. We act wrongly because of avijja (ignorance) and therefore we commit an akusala kamma (unskillful/bad action) that delays or interferes with our spiritual progress. In our ignorance about the real nature of things (in this case, our body) we act in ways that are detrimental to us from a spiritual point of view. Understanding and wisdom will help us refrain from harmful actions, both mental and physical.

In this connection, Buddhism does not recognise that marriage is a divinely ordained institution that suddenly makes sex permissible. Sex is a human activity that has nothing to do with heaven and hell. You will notice that sexual restraint is one of the Five Precepts observed by practising Buddhists. Killing is far more serious because you can hurt another being more viciously. Sex is a craving, just like craving for food, liquor, drugs, wealth, power, etc. Attachment to any of these constitutes akusala kamma because, if we really understand the nature of our bodies and how craving works against us, we will not indulge in it. Buddhism discourages any of these forms of craving because they will tie us down more firmly to samsara. Also, indulgence in sex can lead to other evils like anger, jealousy, remorse and guilt.