SVU was dealing with discussions surrounding trans rights long before they were receiving due attention, and the 2003 episode "Fallacy" is a heartbreaking example of how the justice system has failed the trans community and is subsequently one of the saddest SVU episodes. When Cheryl Avery kills her would-be rapist at a party in self-defense, detectives are taken through the wringer when it's discovered that the DNA found in the bathroom where her attacker was killed that's linked to Cheryl is biologically male.
It turns out that her attacker, Joe, was threatening to reveal that she's trans to his brother Eddie. Feeling threatened, Cheryl struck Joe in the head with a vase. However, tragedy after tragedy befalls Cheryl as its revealed she's estranged from her parents due to her transition, Eddie commits suicide when he finds out the truth, and she is forced to go to a male prison after her sentencing. Cheryl is gang raped at Rikers, and Cabot is left feeling guilty over the whole ordeal. It's a harrowing look at how the justice system needs to change and portrays very real dangers that transgender people face just by being themselves.
While some justice is seen in "Rockabye," the issues surrounding a woman's right to choose severely complicate the overall proceedings in one of the saddest SVU episodes. "Rockabye" sees 16-year-old Lauren lose her unborn child after being severely beaten. Though her father is adamant that Lauren's pregnancy is a result of rape, Stabler and Benson's investigations into her boyfriend Wayne prove to be fruitless. The real twist comes when Lauren tearfully reveals that she was the one who orchestrated her beating.
As it turns out, an abortion clinic that Lauren was attempting to make an appointment at kept dismissing her calls thanks to a seedy doctor that worked there. Backed into a corner, Wayne and Lauren sadly took matters into their own hands. Between Lauren's tear-jerking confession and her subsequent treatment, "Rockabye" is a difficult watch. While the doctor is thankfully arrested for fraud in the end, Lauren still had to suffer in a way that no one should and was the subject of one of Law & Order: SVU's saddest episodes.