None of us are in a position to judge this situation as none of us know - or will ever know - the whole story. Even if we did, who are we?
I just think it's particularly cruel of BB to attempt to shame Cristian like this. He's only just 20 and has signed up for a TV show - not to have his (likely teenage) past dragged up. It seems like a deliberate attempt to humiliate him.
I'm not entirely convinced by the comparisons between this situation and Danny and Marc's abusive tweets. If there was just a couple of tweets, maybe... but there are several and the language used surely reveals something about their character.
That said, and call me a hypocrite if you like, but I'm not comfortable at all when BB bring up what HMs have done outside the house - particularly when only a few of them are targeted. I don't recall any mention of Marc's behaviour outside the house.