I understand that a lot of men state that stimulating the prostate results in arousal, but that's not the case for ALL men. Not all guys (straight or gay) like having something up their arse. Some straight guys like getting fingered, and some gay tops would cry if they bottomed. But can the prostate indefinitely be a source of pleasure? Possibly. But for now we just know that if the anus was biologically meant to be receptive and penetrated, the body should have a system/sexual response that secretes lubrication and relaxes/stretches like the vagina. That's the reason I'm saying that no one's a "natural" bottom.
Right now, I know I might sound like I'm a raging anti-gay, sodomy is sin christian scientists. But I also know that anal sex does feel really good in a way that biology can't explain completely yet. All I can really say is that I love anal sex and dick as much as the next gay guy, even with all that in mind.