I agree with many of the posters here. Back in my straight days (and I'd say this applies to the men I fuck, too) I was thrilled to be inside another human body, because of what it said about me. Thrilled that they trusted me enough--that I was chosen, worthy, special in some way to some other human being. My desire to give pleasure came automatically after that.
You can get similar physical sensations elsewhere. But you can't get the same emotional buzz.
That's why I chose a feeling of manliness. For me, that's kinda what it's all about.