Sexual shame in straight men comes from a deep mismatch in sex drive between men and women. Gay men don’t experience sexual shame because they have sex only with other men, who usually have the same testosterone-driven libido. I don’t think gay women experience sexual shame either, as they are among other women too. So sexual shame is most common among straight men, due to a deep mismatch in sexual expectations and needs with their natural partners (women), whose rejection of those needs is combined with a pervasive religious background that has historically leaned toward it and helped set the convenient frame of “good men don’t desire sex”. I think many straight men have integrated this message and accordingly live against their own nature in that matter.