Men, both gay and straight, can enjoy the intensely pleasurable sensations of anal penetration, when combined with appropriate lubrication and a sensitive lover. But usually male orgasm still relies on penile stimulation. [i] To be capable of penetration the penis must be erect, so a man must be aroused. But the receiver of intercourse never needs to be aroused. Being the receiver of intercourse with a sensitive lover may assist with orgasm by mental association but the stimulation does not in itself cause orgasm.
Heterosexual men assume that the sensations of being penetrated are equally arousing as the sensations of penetrating. They don’t take into account that intercourse stimulates their sex organ but not the sex organ of the person being penetrated. Consider fellatio as a parallel. No matter how amazing the sensations are for a man, when a lover stimulates his penis orally, the mouth is not a sex organ and hence providing oral sex cannot cause his lover’s orgasm. Because of men’s enjoyment of penetrative sex (which defines their sexual role), a woman’s role necessarily becomes one of (crudely expressed) providing an orifice for a man to ejaculate into.
Given their drive (to penetrate) heterosexual men never have to identify with the perspective of the receiver of intercourse. So when they see an attractive woman, men talk about ‘giving her one’ (and they don’t mean an orgasm). Men accept that the role of the penetrating male (regardless of orientation) inherently involves persuading a lover to accept penetration. Most men cannot accept that women are so indifferent to an act that is so acutely arousing for a man. But throughout Nature, the male is motivated to mate. Men’s focus on intercourse is not a choice. Men are biologically programmed to ejaculate into a vagina. Otherwise men could enjoy oral or manual stimulation instead and none of us would be here to talk about it.
The mouth and vagina are both susceptible to thrush (a yeast infection), being warm and moist. These similarities probably explain why men almost swoon if offered oral sex. If cunnilingus provided a similar pleasure, one would expect women to be more willing to offer fellatio in exchange. True arousal would interfere with women’s passive acceptance of intercourse. Both sexes may be aroused by the concept of either being the penetrator or being penetrated regardless of sexual orientation. Men and women also use an artificial phallus to simulate penetration as a turn-on either for themselves or for a lover. Both sexes can receive penetrative sex but only a man can fully penetrate a partner with his engorged sex organ.
[i] … sexual contacts between males of the lower mammalian species do proceed to the point of orgasm, at least for the male that mounts another male. (Alfred Kinsey)
Excerpt from Women’s Sexual Behaviours & Responses (ISBN 978-0956-894717)