It's because it's naughty, bad, taboo, tight, and it's so wrong. I love it. Been a buttfucking fan since I did my high school gf back in 1980. The best sex ever
Not a single argument of her that really would matter. There is simply no easier way to separate a good slut from all that garbage like her than shove your boner between her cheeks and knock on her puckering sphincter. Not a single time ever asked for permission and always enjoyed it.