I think that PIV sex is not always rape (by the current legal definitions and current social norms).
Many of the comments on this thread come across to me as "penis-in-vagina sex can feel good and PIV sex reproduces the species, therefore any harmful effects on women as a class can be ignored".
It's similar to people saying "I like my job, and work finances society, therefore work is harmless to workers as a class" or "hard work never did anyone any harm". On the contrary, hard work has directly killed many thousands of people.
Even if a social practice is beneficial for some people or for society as a whole, I think it can still be worthwhile to examine problems caused by the practice. With the work example, even though a mine-owning billionaire may love his work of clinching deals while drinking cocktails on his super-yacht in Monte Carlo marina and he is very unlikely to die from rock dust in his lungs, we can still question why work is problematic for the male and female miners with lung disease caused by years of breathing rock dust into their lungs.
Likewise with PIV sex. People obviously like sex in a way and at a time of their choice, and that includes PIV sex. Just because PIV sex is popular and also effective at producing children, that doesn't magically make PIV sex always problem-free or have equal risks and benefits for men and women. I think the blog is a useful starting point for examination of various issues, but nobody has to agree with what the blogger wrote, just tolerate that it could be a useful catalyst for our own deeper critical thinking.
I think that men get a better deal out of PIV sex than women do. Some of the reasons are biological/medical and we can do little or nothing to change those, but some of the inequality is social and that could be changed, but only if we offer deeper thoughts than "I'm all right Jack" or "Bollocks".