yuri and yaoi in mangas and animes is abnormal. (the majority of male rape victims don't fall for their assailant and the majority of women don't find toe sucking to be sexually arousing)
yuri and yaoi in real life is normal and one can find many instances in nature that occur naturally (look for new mexico whiptail *an all female species of lizard* and corbicula clams *physically a hermaphrodite but genetically an all male species of clam*). With humans homosexuality occurs on a epigenetic level (so they are predisposed to it, but even then it's not a guarantee that you'll become one)
On a personal level my religion says it's a sin to God but it also says that I'm not to judge anyone nor condemn anyone for any sin so to all who are homosexual I applaud you for your bravery to face great challenges just don't do public display of affection in front of me since I'm uncomfortable with it even if you were straight (I'm ok with hold hands, hugging and light kissing but don't go sucking on each other's face or moan so loud)
Back to DD, I think it should stay the way it is because everyone should have their freedom to express their love to anyone(even if it is of the same gender) in any way they want (as long as they don't disturb anyone in public) even if it is in the most un-romantic thing ever called DD. If you're uncomfortable having to potentially DD with someone that is of the same gender then just do DD with people you know and find a girl irl that is willing to DD with you^^.