It is a normal human function. I think something becomes pornography in what context it is placed in. It would be nice if people could be mature about sex, instead of being a bunch of twisted puritans who suppress their sexual energy in a negative way, creating all sorts of perversions. It is also a normal human function to defecate. After giving it some thought, I think you should write that letter after all.
Any adult knows perfectly well what the male orgasm is and looks like.
I think not. Being mature about sex is precisely the issue here. Your need to show such events on film is immature by it's very nature. Why don't your write me back with the title of one single commercial film which shows an ejaculating penis on-screen which is not in the realm of pornography. I'm afraid you won't find it here.