First of all, the title IS dumb. I don't believe in cheating, I know that the act of cheating exists.
Now, forget the sexual/reproduction part of it for a second.
When you enter into a relationship with someone - particularly a monogamous relationship where both of you are living together and probably married, you are agreeing to spend a certain amount of time, energy, and money/resources on each other. It's much like a work contract where you get hired and the company agrees to pay you for the time and energy you put into the company. Cheating in the sense of a relationship is rather like being caught out at fooling around at work - you will be assumed to be 'wasting' the resources being invested into you. It's a break of trust, as no one and no company wants to feel like the time and resources they give to someone else are wasted, and by extension unappreciated.
I think it is wrong because of this.
Some people have arrangements with relationships to either have open marriages or open committed relationships, with the understanding that the partner will be honest, safe, and not let these other commitments infringe upon their major commitment. Those are fine too. The key is communication and honesty. I know from experience that those people and their spouses or partners do not consider it 'cheating'. 'Cheating' implies a break of trust/rules. If trust is there and the person is free to do what he or she chooses within whatever strictures of that relationship they hold, it's not cheating.
If you wouldn't cheat, then I'm not exactly sure why you asked this stupid question.
Now, forget the sexual/reproduction part of it for a second.
When you enter into a relationship with someone - particularly a monogamous relationship where both of you are living together and probably married, you are agreeing to spend a certain amount of time, energy, and money/resources on each other. It's much like a work contract where you get hired and the company agrees to pay you for the time and energy you put into the company. Cheating in the sense of a relationship is rather like being caught out at fooling around at work - you will be assumed to be 'wasting' the resources being invested into you. It's a break of trust, as no one and no company wants to feel like the time and resources they give to someone else are wasted, and by extension unappreciated.
I think it is wrong because of this.
Some people have arrangements with relationships to either have open marriages or open committed relationships, with the understanding that the partner will be honest, safe, and not let these other commitments infringe upon their major commitment. Those are fine too. The key is communication and honesty. I know from experience that those people and their spouses or partners do not consider it 'cheating'. 'Cheating' implies a break of trust/rules. If trust is there and the person is free to do what he or she chooses within whatever strictures of that relationship they hold, it's not cheating.
If you wouldn't cheat, then I'm not exactly sure why you asked this stupid question.