i want to clarify too, what "getting normal about casual sex" looks like
the hookup culture in mainstream society in the US is NOT normal
it's polluted by sex negativity and it often manifests by people feeling ashamed or guilty after casual sex and this is why people say that having sex "makes it weird" and "ruins friendships"
being "normal about casual sex" looks like:
maybe you had sex and it wasn't good and you don't want to do it again but you can laugh at it with that person and it is still a positive experience in your relationship with that person, like "haha, remember that one time, oh wow that sucked we are so sexually incompatible haha" and then you can keep going on as-is whether you're friends or acquaintances or whatever
maybe you had sex and it was great and maybe you start having sex regularly. maybe you initially had casual sex outside a relationship, but later decide that you are interested in the person more seriously and want an actual romantic relationship with them. maybe you never want a relationship with the person. either way is okay
maybe you had sex and one person thought it was good and wants to have it again but to the other person, it sucked and they don't want to have it again. and because both people value consent and respecting boundaries, it is totally fine. there is no pressure from the person who wants sex again, to have sex again, they accept no as the answer and they are normal about it. if the people were friends they keep being friends. the "rejected" partner does not withhold affection or cut the person off in response to being told no.
there are other ways to be normal about casual sex, these are just some examples. but what is NOT normal by any stretch is:
being unable to look people in the face after having sex with them
feeling ashamed or guilty when reminded of the fact that you had sex with someone
pressuring someone to have sex
ghosting people after you have sex, in the absence of extreme, boundary-crossing behavior that would warrant ghosting in a non-sexual setting