I am saying this from a fanfic Barty perspective not a canon Barty perspective.
Barty's family was not a blood supremacist. His father was literally the minister of magic. Even if he didn't have a good relation with his father if he was a good friend he could have used that power to save Regulus from his family and being a deatheater. Instead what he does is he jump to become a deatheater (wizard terrorist) just because of his grudge for his father.
He didn't had any pressure to become deatheater unlike Regulus and Evan. If people can blame a teenage Sirius for running away from his home where he was physically and mentally abused then why did Barty get away with doing this just because he was a teenager. Even Regulus doesn't question Barty while he holds a lifelong grudge over Sirius. Jumping on the sea to drown with your bestfriend instead of saving him while you have the power isn't a sign of good friend or even good person.