This pretty much answers your question outright. Whilst it's common, it doesn't make it more acceptable. It's just your body reacting to sexual experiences in a way your body will react. The sexual organs lack any sort of brain to stop reacting to negative sexual experiences or positive, and, they certainly aren't a factor in determining rape since a sexual organ solely cannot give consent. It just reacts in the way it's supposed to. You can't stop your sexual organs from responding in the way they are supposed to function. It'd be akin to saying you trained your heart to beat normally during terrifying situations when your heart beats faster. Or that you trained your lungs to continue breathing when you're out of breath or get the wind knocked out of you. As detailed in the link above (and more articulately than I could ever state it as) it's just not possible. Inversely, you can't be train yourself to get pleasure from sexual acts that give you none.
If you're getting raped you might as well go with the flow and enjoy it. I'm not saying rape is a good thing, but if you can't escape it, why not enjoy it? It's just gonna hurt more if you keep fighting it.
If you're getting beaten you might as well go with the flow and enjoy it. I'm not saying getting beaten is a good thing but if you can't escape it, why not enjoy it? It's just going to hurt more if you keep fighting it.
If you've been lit on fire you might as well go with the flow and enjoy it. I'm not saying getting lit on fire is a good thing but if you can't escape it, why not enjoy it? It's just going to hurt more if you keep fighting it.
If you're being stabbed you might as well go with the flow and enjoy it. I'm not saying being stabbed is a good thing but if you can't escape it, why not enjoy it? It's just going to hurt more if you keep fighting it.
If you've been forced to take out the trash, you might as well go with the flow and enjoy it. I'm not saying being forced to take out the trash good thing but if you can't escape it, why not enjoy it? It's just going to hurt more if you keep fighting it.
If you've been forced to attend a crappy musical based off a Disney film you might as well go with the flow and enjoy it. I'm not saying being forced to attend a crappy musical based off a Disney film is a good thing but if you can't escape it, why not enjoy it? It's just going to hurt more if you keep fighting it.
If you're house is bombed you might as well go with the flow and enjoy it. I'm not saying getting your house bombed is a good thing but if you can't escape it, why not enjoy it? It's just going to hurt more if you keep fighting it.
If your teacher gives you a failing grade you might as well go with the flow and enjoy it. I'm not saying getting a failing grade good thing but if you can't escape it, why not enjoy it? It's just going to hurt more if you keep fighting it.
Do you see what I'm getting at? Why is rape so different from these other things that you're suddenly forced to enjoy an all around negative action that
never has any positive results to a horrific action that isn't even their fault in the first place. I suppose we should all go with the flow and enjoy any action that happens to us in our lives because it's just going to hurt more when we keep fighting it? Brilliant logic. I'll be back after I hop in a time machine and tell all of those African Americans striving for social justice back in the 1860's onwards that they might as well go with the flow and continue being treated like crap because it's just going to hurt more if they keep fighting it.