He is not being charged with rape. He is being charged with intentionally tearing a condom during consensual intercourse. It's pretty offensive to compare this with rape, imo.
Actually, he's not being charged with anything yet. The warrant is simply to require him to come to Sweden for questioning, after which time the prosecutor will decide whether to charge him with any crime. At the moment, he has only been accused of a crime.
Also, it is my understanding that the accusation was brought by the police officers after reading the statements given by the women in question. They had only come to ask if Assange could be required to take an HIV test.
The questioning relates to exposing a woman to bodily fluids against her will, creating in her the risk of disease or unwanted pregnancy.
She may have agreed to sex given certain conditions, he (allegedly) wilfully broke those conditions. There may or may not have been coercion involved but rape is a good shorthand description and there are serious questions to answer and serious charges to be laid if he cannot provide good answers.
That is actually quite clearly defined as rape in Swedish law: 'Causing helplessness or a similar state of incapacitation shall be regarded as equivalent to violence.'
Also, it is my understanding that the accusation was brought by the police officers after reading the statements given by the women in question. They had only come to ask if Assange could be required to take an HIV test.