In the Guardian article you refer to, he explicitly said that people shouldn't be criminalised for "looking at things".
By which he meant CSA. He wrote that in 2003.
The Hunt For Britain's Paedophiles was broadcast in 2002, and the immense harm done by CSA was very much discussed in the year afterwards. It changed a lot of attitudes and led to demands for change. That's the context for Liddle's article.
Yeah, I will believe a man who advocated for decriminalisation of viewing CSA images - and punched his pregnant girlfriend - when he says he wants to rape under-16s. Talk about hiding in plain sight.
So many men attack others when they have guilty secrets themselves (see, for example, how many men claiming to protect girls from trans people, gay people or Muslims, turn out to be paedophiles themselves). I wouldn't be remotely surprised if some very dark things emerge about him.
Projection is real. I was heavily pregnant when THFBP was broadcast and have never forgotten the convicted paedophile who campaigned for an end to FGM. I think of that creep every time a transphobic man sends me his repulsive rape fantasies about 'little girls showering naked with men'. Ugh. (When you're parent to a trans kid, those dangers show up a lot.)
There's so much else with Liddle. His repulsive, homophobic comments about gay sex, the article attacking Rosie Duffield for discussing her experience of domestic violence, his dismissal of the Rohingya genocide (the mass rapes and burning alive of women & little girls, after their families had been shot) as 'a bit heavy-handed'....