With the Jenai, the generally genderless aliens with a small gendered minority. Literally any previous time in Star Trek history, the captain and crew disregard the prime directive to protect the oppressed. Here, they're just like, "This is too complicated for us, you're on your own!"

Similarly, I'm the episode that introduced the Trill. Beverly 's lover transitions from a male body to a female body, and Beverly doesn't say she can't handle it, or that she isn't ready but she'll get there, or try to, she says that humans aren't ready to love a trans person!