Handbagcrab
You seem to be under the assumption that the bloke knew he was having sex with someone under-age. He didn't. He thought she was of age, seeing as she'd told him that and EVERYONE who met her thought she was older than 12.
I've known 20 year olds who act like they're 12 and 12 year olds who handle running a house because their parents are disabled and they seem far older than their years.
Yes, things could easily go wrong as happened in this case, but I don't really think it's fair to say that 19 year olds (as he was) shouldn't be having sex with 16 year olds.
The age of consent is 16. She was out in a city centre, drunk, at 4am. He spoke to her and conversed with her. Based on all the evidence around him, he had no reason at all to believe she was anything other than the age she told him. That's why the judge did not hand a custodial sentence - he did everything that you could reasonably expect a partner to do (short of checking photo ID) before having sex.
Like I've said - the guy is a convicted sex offender now, and there's no question about that. But we should now focus on what failings happened that allowed a 12 year old girl to be in that situation in the first place.