Eating Chocolate is Unnatural

Someone tried to argue that homosexual acts are unnatural, essentially immoral, because as he explained, procreation is the purpose of sex. Well, it turns out we do a lot of things that are unnatural that most people would accept as moral, so I responded in the spirit of this quote, "A fool tries to persuade me with his words, the wise man persuades me with my own":

Let me get this straight. Eating chocolate is unnatural. The natural purpose of eating is to survive, that is evident. Eating chocolate is an action only taken to attain pleasure. People who eat chocolate aren't doing it for the purpose it is clearly designed for: survival. Eating chocolate corrupts the biological intentions for the act of mastication. Therefore, eating chocolate is antithetical to the natural purpose of eating and therefore is unnatural and immoral.

Not to mention that any seasoning that isn't a means to the end of survival would also be considered unnatural since the only reason we use them is to make the act of eating more pleasurable. Seasonings would also be a good example because of the added benefit that humans are the only species that I know of that flavors their food so it could genuinely said to be "unnatural." Similar examples could be made between drinking to stay hydrated, and drinking soda or beer would being antithetical to that end. This seems like a silly method of determining morality.

I think I'm missing something because I suspect you don't equate eating a seasoned steak to be as immoral as homosexual acts. So what am I missing?

Someone mentioned that chocolate might have some health benefits so I switched it to the "Doughnut Defense":

The only point that is important is that at a certain quantity, it becomes unhealthy, and I didn't think anyone disagreed with that point. If they do, then they can substitute chocolate with something from this site. Now that I think about it, I might as well substitute chocolate with doughnuts so I can call my analogy the "doughnut defense."

In case you think there is something healthy about this sugary toroid, "'When it comes to health, the only thing good about them is the hole,' said Carla Wolper, nutritionist at the New York Obesity Research Center."

Additional Counter-examples:
Outline
1) The action corrupts a natural act, by being the means for an end other than the end it was biologically designed for.
2) The action was biologically designed for a specific end. You do the action in the same way as it was designed for (it would imitate the way the action would be performed to fulfill that end), even if it does not fulfill that end.
3) An action is wrong (or unnatural) if it fulfills the requirements for 1 and does not fulfill the requirements for 2. Otherwise, it is right (or natural).

Example 1
1) Adrenaline was biologically designed for the means of "fight or flight," a means for the end of our survival.
2) Riding a roller coaster corrupts this natural act by fulfilling an end (pleasure) other than it was biologically designed for.
3) Releasing adrenaline from riding a roller coaster does not imitate the natural act of releasing adrenaline, such as seeing the sight of a predator or being inflicted by an injury.
4) Therefore, riding a roller coaster is unnatural and immoral.

Example 2
1) Adrenaline was biologically designed for the means of "fight or flight," a means for the end of our survival.
2) Acupuncture corrupts this natural act by fulfilling an end (pain relief) other than it was biologically designed for.
3) Releasing adrenaline from acupuncture does not imitate the natural act of releasing adrenaline, such as seeing the sight of a predator or being inflicted by an injury.
4) Therefore, acupuncture is unnatural and immoral.

Example 3
1) Toxins are biologically designed for the means of killing other animals, a means for the end of survival of the host species.
2) Using toxins for antidotes corrupts the natural act by fulfilling an end (helping the predator species) other than it was biologically designed for.
3) Consuming an antidote does not imitate the natural transmission of toxins.
4) Therefore, using toxins for medical purposes is unnatural and immoral.

I hope this demonstrates that something being unnatural does not mean it is immoral. Not to mention the number of natural immoral actions one could justify using this system. The next point would be, it is nonsensical to say that biological structures are designed. They may serve some purpose currently or in the past, but to say that they were designed would be to propose an illusory cause for these structures.