I like this "well Danny and Cersei had 'lesbian times'" argument because it proves again that people don't realize the problem and are just looking at it as sex.
Danny's "encounter" was at an age where people can often have doubts on their sexuality, and is most when you can expect someone to be bicurious, starting as early as the beginning of puberty and up to their late teens or early twenties. Her "encounter" also had a literary purpose; it marked a time where her life became less dominated by men, when her brother and her husband were no longer in charge of her, and when she could decide what exactly she wanted to do in her life. In the end, she decided she could be the strong ruler and the bottom in bed, or top, or however she rolls most of the time.
In the case of Cersei, it's said multiple times that she controls people with her sexuality. It's said by Tyrion that her greatest weapon is her cunt, or something along those lines. She has her "encounter" when she's beginning to doubt if she'll stay queen, and begins to fear the prettier queen to come in her prophecy. She realizes that her greatest weapon, the tool she's used to control men for years, would not be able to easily dominate someone like Margaery.
Now, in the case of Yara, what exactly does it mark? Was someone suppressing her sexuality in the Iron Islands and arriving in Volantis let her break away? Then why stay in the Iron Islands? Doesn't she do what she wants? That just makes no sense. I hope you all realize a truly or predominantly straight person will not have sex with someone of the same sex "just because they can and because they do what they want." They would have to want to in order to do it, and if they don't want to, they clearly don't do what they want. So, the show made her a lesbian (or bi), to prove... absolutely nothing. No matter how I would word what they did, it ultimately comes out to "it was sexist," or homophobic in the sense of ignorance of how homosexuals are.
God this anti-argument is cancer. Open your eyes, sheeple. Accept that it's on the spectrum of wrong.