Why are periods considered so nasty?

Get ready, I'm about to vent.

Why is it that the whole of the population thinks periods, or period blood, is so vile and discusting as compared to normal blood? I just met someone who said he'd rather stick his hands in feces, than period blood. Are you kidding me? To me, its just blood. Yes, it smells different than regular blood. Yes, it has chunks of lining in it. But I'm so sick of the on set of a period making your friend "Betty Sue", suddenly into a leprosy victim. It's particularly sickening when you observe this kind of behavior in partners. It's just blood, people! It's just like the ridiculous queef vs. Fart story. Because it comes from a vagina, it's suddenly discusting Because your expelling of various gas waste thats been swimming with your turds isn't?!