One difference betw. RSPCA and IWF
At one time the theory of English lawmaking was that the law merely made explicit what everyone already knew and agreed was illegal. It was the formal expression of the consensus.
By that standard, one can understand the RSPCA's quasi-police powers: pretty much everyone agrees (these days!) that cruelty to animals is A Bad Thing And Contrary to Law.
The IWF, in contrast, represents a very narrow view from which a good many people dissent. For all the yammer about protecting the children from porn, I have yet to see any study that persuasively makes the case that porn actually harms kids.
Two reasons for my assertion: first, the human mind is a good deal more resilient than the Nanny State and its minions would have us believe. While a few weak-minded souls may become traumatized from a graphic depiction of Tab A being inserted into Slot B, most will not.
I imagine some will become sexually excited (but what's wrong with that?) and others will yawn "Oh, that's how it works, ho hum", but very few, if any, will be rendered dysfunctional or become hopeless lust-a-holics.
Second, it may actually be good for kids to see porn, because it helps dispel the aura of shame and "dirtiness" that the blue-stockings like to surround sex with. I notice from time to time news reports of young people coming out as gay at surprisingly early ages; one cannot help but wonder if this is because the intertubes clued them into to the fact they are not alone in the world in preferring boy-boy or girl-girl romance. Porn may very well be a part of that.
Really, the squawking about porn harming children is much like the silly health and safety rules of the UK right now: it's all about vague possibilities, mights, and maybes, not about behaviors which actually, provably have caused harm.
Is there anything else I can say to overturn the shibboleths of the NuPuritans and their Stasi-oid bolshevist friends?
PS: When the NuDispensation takes power in Britain, with Sarah Bee as Ministrix of Deportment, all health and safety rules will require re-justification via a rigorous cost-benefit analysis. Rules against behaviors that have caused few injuries or deaths will be rejected toot sweet. Even harmful activities will be given a green light if they are culturally valuable.
Take that, vile nanny state!