Which political point? penis goes in vagina?
A crude depiction of a soldier fucking another soldier in the ass was how the westboro baptist church protested gays in the military.
It could be used to protest circumcision or FGM.
It could be a crude sign used to mock a political point like the dildo Isis flag, or Obama's O symbol turned into Goatse.
But moreover, a piece of porn could be part of a larger work, where it becomes part of the art. For a crude example, many of the crude jokes in south park. For a less crude example, the 'porn' might be a part of the love story between two story leads.
I could go on, but the idiocy of this point has been well shown by now.
Congrats then. You've banned the bible. I suddenly see why the progressives will be on your side here.
There you go, there is your "impossible to define" definition. All it took was one person, 5 minutes of effort, and a 3 people trying to poke holes in the definition so it can get refined (in the same 5 minute period)
Watch me poke holes in it again: see above for examples.
Also, judges will intentionally define softcore porn in a way that benefits them. That's why you give brightline rules, so they don't get the leeway.
And it still completely fails, btw. Girls gone wild? Not porn, as it's technically clothed. The book teaching how kids can give oral sex? That'll be fine, as clearly it's educational literature. But a neoclassical sculpture? PORN! ALL THE PORN!!!
Quite bluntly, you don't have a leg to stand on here. And as your definition gets more complex, the bigger problem will occur: no law will be enacted as you envision it, nor interpreted that way, and the more complicated the law, the further the two diverge. So even if you design a perfect law that manages to only describe what you consider porn, and not what others consider porn, what will be enacted will be something that limits free expression drastically. This won't be an accident,
this will be purposeful. There's nothing the government hates more than free expression, so they'll take any excuse, any loophole, and try to completely destroy any protections to speech at all.
They'll look at the complicated porn ban, it'll become a ban on anything with genitals in law, enforced by an agency that will use this law to regulate 'hate speech', which will then be interpreted as covering speech criticizing the government.