But — vitally — means the partner did not consent to the sex that was had. It disgusts me how many people are arguing that non-consensual sex isn't rape if they were willing to do it under different circumstances.
I don't think anyone is suggesting what you are insinuating that they are suggesting.
The traditional definition of rape is "by force and without consent". Not to say this isn't immoral or indeed criminal, but it isn't rape and to call it such is unfair both to him and to rape victims.
That's the traditional definition, but it's neither a good nor a modern one.