Total Bullcrap... me and wife watch porn together all the time... and trust me her tastes in it are different than mine but we both entertain each others fantasies and desires...
Watching porn has helped her be more upfront in what she wants and how she wants it. That lets me cater to her specific tastes a little better and vice versa. We have a much more diverse bag of tricks so to say in that we try different things that strikes the others fancy that we see in porn... those we like we try again and again.
Sure beats the poor soles that think sex is only missionary with the woman on her back.
Variety is the spice of life. That's why after 17 years of marriage sex is better than it ever was. And way better than it was in the beginning for both of us.
Notice I'm not saying watch it alone in private. But together.