I was quoting that (along with the other three quotes in that section) as 'web wisdom'... common things you'll hear around the Internet. That is not my position. My general position is "casual sex is a natural sorting method women and men engage in to discover what caliber of partner they can secure", as discussed in my article on satisficing. I don't think it is usually harmful.
A woman who's engaged in a lot of casual sex is generally a red flag for a guy looking for commitment. It's not so much that sex damages the woman as that a lot of sex tells you a woman may be unclear on her mate value and won't be happy with any man she's good enough for. That's not always the case (sometimes she's just a sensation-seeker... which can present other problems for men wanting an LTR). But it is often enough to be a flag for men who want monogamy. The sex is much more symptom than cause, however.
I'll still do an article on it. There's some nuance and it's worth fleshing out.