Honestly, I spent many years and many partners later, experiencing shame with period sex which is absolutely insane to me now.
Period sex is the best, it feels amazing, it is extra lubrication and I find my body is hyper sensitive (physically, in a good way). Plus my argument is always - The vagina cleans itself?! Cleanest blood you could get your hands dirty with! AND if they just want to enjoy the ‘good’ parts of the pussy, they don’t get to enjoy it at all.
Don’t get me wrong - if you really aren’t into period sex, you shouldn’t be shamed for it but it is the way that you react to it is where the problems arise. If someone can openly and honestly say ‘I don’t think this experience will be good for us because I am not completely comfortable doing it and I want to give you my 100% best’ ;) I’m going to let it slide. If someone is just like ‘ew, no that’s gross’ I’m going to sit you down, give you a serious lesson on the anatomy and then never have sex with you again.
I have been lucky, most of my sexual partners have been extremely nonchalant about period sex - my shame came from the ones who acted nonchalant but as soon as they came I was hit with it being gross and some dumb, screwed up look on their face. The same people who will cum on your face, no worries. You cum on/in me, I period on you, it’s simple and fair.
The best way to become comfortable with period sex is to masturbate, it’s totally fine, a bit of blood, pop a towel down! Do it in the shower! Wear a sea-sponge/condoms! There’s so many ways around it.
Whether you’re into it or not, that’s okay, just don’t make anyone feel badly about it. Period.