Rape is about power.
If you want more than a quip, consider this...
You're a child. Day in and day out, you're oppressed by someone. It could be the local bully. It could be gang members. It could be a family member or friend. Something torments you every day. Your family isn't supporting you in your time of need.
So, you internalize.
Your mind starts to process what's wrong. You're ashamed to talk about it, but even if you could, would it change? You rationalize that it wouldn't. You rationalize that the person is stronger. You long to feel that strength. The victory over someone or something weaker than you.
You see her there without knowledge of your pain. Fixed on her, you size up the risk of overpowering her. You're very intent on feeling that power. You watch until there's that sign of weakness where you believe you can have your success. Your 'victory'.
She has no clue what hit her.
Afterward, she's damaged for life, but all you care about is the rush of having exerted yourself over someone. You're no longer the victim. You're now the strong one. It feels good. As the high from your deed dissipates, you want to feel it again. Someone else unknowingly catches your eye. The cycle starts over.
Most rapists are mentally damaged.
Most rape is about power.
All rape is damaging (hence evil).
All rape dehumanizes the victim by reducing them to the pursuit of a feeling/achievement.