So, at some point before he fell (pre-war, during his first captivity, on a mission with the Commandos) Bucky was raped. Steve knew about it & did his best to help him through it, but that was about all the support system they could risk-- back then, male rape wasn't a thing that was ever acknowledged. It wouldn't even have really been an option for them to open up about this awful thing that happened to anyone else, even the Howlies.

So when Steve wakes up in the future and finds out about all these organizations supporting and advocating for rape and abuse victims, he thinks it's absolutely amazing. He starts getting involved, speaking publicly in support of victims, and talking about his strong, brave, wonderful friend Bucky who had to go through this all alone, and how great is it now that there's all these people who are willing to stand up against sexual violence? It's a little bit of a violation of Bucky's privacy, but he doesn't think Bucky would mind too much if it helps others in the same situation. And besides, he's dead and this can't hurt him anymore.

...Oh, wait.

Meanwhile, the WS actually isn't used like that, but now that the idea's there...

And all the lovely awful aftermath of accidentally causing Bucky to be abused again