Yes, I'm aware. It makes perfect sense that it shouldn't just freely give an endless home to every weak sperm.
That is not exactly how it works. That was a test you did not pass. I wanted to know if I made a vague statement that was only just technically true, if you understood that part of a woman's body (and the life cycle of sperm) well enough to refine my words.
A vagina is acidic. This has nothing to do with sperm selection. This is about disease prevention.
It is unclear how female orgasm impacts pH, but the presence of semen begins a countdown. Within 10 seconds, part of the vagina will adjust pH. It can go from as low as 4.3 to as high as 7.2, if my memory of the science is correct.
An acidity of 4.3 would take less than a minute to degrade sperm to the point of uselessness. Moreover, white blood cells arrive and begin attacking any foreign body, any at all, including sperm, within seconds. Luckily for semen they have a few layers of protection, because it can take as long as a week for them to get their shit together, fight through the cervical mucous, traverse the minuscule cervical os, and still have one shot in thousands of being among the hundreds to choose the correct fallopian tube. Only one tube presents an egg, and the egg signals its presence. Forcing sperm to choose is about quality sorting, not the woman's immune system. The immune system is always about disease prevention.
Sperm rely on fructose for energy. They cannot access this energy supply (which they bring with them) until they find the uterus and shed their protective layers. So, they move fairly slowly. Finding a fallopian tube lights a fire under them. In order to do find one, they must shed their protective layers. The ability of the man's semen production process to provide enough cholesterol and fructose to protect and feed the sperm, is about selection. For real, don't get it twisted.
If you want to leave your DNA behind forever in a woman's body, you will have to impregnate her with a male offspring. Only then will your mitochondrial contribution remain, and only after a specific stage of fetal development. You need to understand that the vagina is a miracle and a wonder. If your body wanted to attempt to leave DNA behind, that pussy would just obliterate it. Whatever the immune system left behind would be devoured by yeasts and bacteria.
The women here are well read on a number of subjects, and have a wide range of professional experiences. If you want to discuss science with us, you will have to actually understand the science, or be asking us to teach you. In this case, you are doing neither. It makes me wonder.