Individuals are more likely to commit atrocious deeds if their society does not actively discourage them.
Does living in a society that turns a blind eye to racism acquit the person who chooses to set fire to a bus full of black people? Absolutely not! That person is still a monster, a murderer, a terrorist. That person deserves an appropriate punishment for his/her crime, and absolutely no less.
The fact that that individual is responsible for their own individual actions, however, does not acquit the society that created conditions favorable to those actions.