Women, in my experience, have proven themselves to be fully capable of what men can do, and not just in physical terms. Women can learn and comprehend faster than men can too.
Where they are not as strong as men, they can certainly be faster, and that makes a huge difference in a fight. They are capable, so why not?
If they wish to fight in an MMA, that is fine by me, it is their choice, again, if people don't like it, they don't have to watch it.