Producing

Ethically speaking, it should essentially come down to consent and lack of harm. And if, hypothetically, we were inventing the laws from scratch, then I'd suggest restricting images which contained actual sex acts to the individuals themselves - i.e. allowable, if mutually desired, between lovers within relationship to each other, but not to be traded/sold/distributed. That would respect the sexual privacy of relationships whilst providing a safeguard against an abuse potential.

Viewing

[Not advocating anything here, this is purely theoretical, laws aside, etc.] The act of viewing a picture is in itself inconsequential. Viewing a picture need in no way contribute to supply and demand, but it could do so depending on the context. If it did, then it would, IMO, be sensible to apply a general principle, which should be applied to *any* consumption of *any* product: first get assurance of its ethical provenance.

I don't believe there is anything at all wrong with wanting to look at ethically produced beautiful/sexy pictures of girls. In fact, the opposite really. If, OTOH, someone wants to look at and get off on photographs of abuse and harm, whilst their action in doing so is not itelf causing the harm unless linked to demand, it is revealing something very wrong and sick within them...