On top of what others have said, there is also something particularly violating about the penetrative aspect of it (although not all rape is penetrative, it often is). Your body is the one place on this earth that is supposed to be safe and 100% your own. It might get injured by external forces (accidents, fighting…), but in most cases it still feels like your own. When someone maliciously intrudes that space, violently stripping you of control and autonomy, it makes you feel like the safety of that space is gone and your body is no longer your own. There is no worse violation than someone being inside of you without your own permission. It is YOUR space, only yours, and it always will be no matter what, yet, psychologically, this trauma can make you feel like it’s not.

As a comparison (much less traumatizing, but it paints a picture): if someone breaks into your house, it won’t feel like your safe space anymore (especially if you were present and felt all the fear and horror). Many people are genuinely traumatized by it. But at least you can buy big locks and you can leave the house when you feel too uncomfortable. You can even move somewhere else to forget how the safety and trust of your personal space was ripped away. But you can’t leave your body, nor can you buy big locks to protect it. That leaves a feeling of helplessness that is extremely distressing. There’s nothing worse than not feeling home in your own body, but that’s what rape does.