Santana is a fucking bitch. She has told people to kill themselves, she has constantly bullied every other character on the show. She has stabbed everyone in the back and never faced a consequence. Finn didn’t ‘out’ her on purpose, he just hit close to home with her own medicine. He called it as he saw it without insulting her, just telling the truth. It wasn’t his fault that someone overheard. 

By some of the fandom’s comments, it’s as if Finn is the worst person in the world and Santana can do no wrong. No one deserves to be outed like Santana was, but it’s not Finn’s fault. And it seems as if because this one bad thing is happening to Santana, it doesn’t matter what other horrible things she has done before.

My 2 cents worth. Disagree with me if you want.