If these were reducing options--if you could only find anything a woman could run in with a little skirt on it--then I would grump. But they're increasing options. It's like when my friend's kid wants to wear the same uniform trousers as the boys at her school: I am on the side with more options. (For the record, I think the boys ought to be allowed the same uniform skirt as the girls if they want it.)
Also: the companies that make running skirts make other clothing for women that allows for freedom of motion and ease of care. While it would be just lovely if we lived in a culture where those elements were reasonably available in all women's clothes, in fact we don't. Having clothing in which one can be both femme and active goes both ways. Having people who are thinking in terms of "the person in the skirt is a badass" ramifies both ways.