Speaking as someone who has discovered things of a seriously awful nature about two close relatives, I can't simply forget the times I spent with them when they just seemed like fun, loving people who shared my sense of humour. I still can't get my head around what I was told, two and a half years after being told it.
There's a word - 'enormity' - which often gets misused. People think it refers just to size, when in fact it's more synonymous with 'atrocity', and it means specifically the great magnitude of something deeply morally wrong. And the idea of someone you love doing something like this is just enormous to take in: confronting the reality of it is impossibly painful. Being unable to confront that reality isn't cowardly, and if you think it is, then just wait until it happens to you.
So I don't condemn or judge his family for defending him, or for being so far down the path of denial that they're trying to rationalise his behaviour. One day, maybe, it'll finally hit them that he did something very, very wrong, and they'll wonder what the hell they were thinking. But it's not up to us to decide when that day should be.