That comes close to what many old people say "its ok to be racist, because when I was young, everyone was racist and we thought it was OK"
Not true. you never have a situation where everyone agrees that bad things are OK. Someone always questions them. eg in the 18th century, there were people in the UK campaigning against slavery in the US, at a time when the apathetic accepted it as the norm.
It is NOT ok just to drift along with the majority - eveyone has a moral duty to ask themselves if things are right or wrong. And confusing the issue by saying that we cant define right and wrong, is just a fudge.
How about this as a principle: allowing others to do bad things is as bad as doing them yourself.