okay, follow-up to this post
you, personally, can feel that sex is a casual activity without any special significance. That's fine
However, a person's physical body is, I think, very, VERY different than their car, an hour of their time, or a book you borrow from them.
If you borrow someone's book and don't give it back, decide to hike the trail you want instead of the one your friend wanted to hike, or refuse to turn off the music in your car that your friend hates, you're a bit of an asshole but you are not a rapist.
If you give someone food and lie about the ingredients to trick them into eating it, you're still not a rapist but you've done something horrible. If you know someone hates hugs and you hug them anyway, you're creepy and people should stay away from you, but it's still worse if you know someone doesn't want sex and you make them have sex anyway.
Consent should matter throughout life, but consent in regard to a person's body carries more weight than respecting their preferences about things external to them.
If we framed sexual consent as basically the same as respecting someone's choice about what movie they want to see or what store they want to go shopping at, that would be really bad.
Whenever I've brought this up, it seems like I get "well, you shouldn't coax your friends do other stuff they don't want to either!" which seems a little out of touch with reality, because there are occasions when people decide to be a good sport about something they don't enjoy for the sake of someone else, and if that thing is a bad romantic comedy movie, it's very different than if that thing is sex.
Now, can people with a healthy sense of their boundaries approach sex with the same framework? Sure, if they want to. Should this be the default approach to sex? HELL NO.
I think that healthily having a "casual" attitude toward sex where it is nothing "more" than just another activity requires a good sense of your own desires and boundaries and confidence in asserting them. "Sex is just another thing you can do with someone" is good for people who know themselves well enough to feel secure and confident making that call, but it sucks as a starting point for defining the significance of sex to humans.
Something that involves letting another person within the personal boundaries of your body doesn't have to have a "special" significance to it, but you have to undergo the process of figuring out what significance it has to you. Does that make any sense