Men can't help themselves. Sexual assault and rape occurs when a man is sexually frustrated and becomes so excited that he can't control himself. Many assaults and rapes are premeditated and planned. Many rapists state that they could have had sex elsewhere but preferred to rape. Rapists often are not sexually excited.
Rape is an aggressive and violent act.
It seems that sex is used as the most effective way of degrading the victim but the motive has more to do with power than sex. Women provoke assault or rape by the way they dress or act. Almost anything a woman does could be construed as being an invitation, or 'asking for' assault or rape. Women who are affected by alcohol and drugs are asking to be assaulted or raped. Being in a vulnerable situation does not imply consent.