Nobody here is dense but you.
As with the English version of the law there are a vague and ill-defined set of stipulations that:
"An image is extreme if it depicts, in an explicit and realistic way any of the following—
"(a)an act which takes or threatens a person’s life,
"(b)an act which results, or is likely to result, in a person’s severe injury,
"(c)rape or other non-consensual penetrative sexual activity,"
The first problem here is that just because it is "realistic" does not mean it is *real*! Consequently a staged photograph which was actually taken will every possible safety precaution observed could *still* fall foul of this law because it is "realistic".
The second problem is what "threatens a person's life"? This is entirely subjective and relies on someone's *opinion* of what it looks like is happening in a picture, instead of what *actually* happened.
Look at some Goth imagery and you'll often see pictures of young ladies in erotic poses in floaty white dresses who are being threatened with knives of have apparently had their throats or wrists cut because they're covered in (fake) blood. Now again if that looks "realistic" it could be covered by this law even though nobody was harmed in the making of that picture.
The same goes for "severe injury" which, in the Scottish case is even broader than the English law which at least only covered injury to the "Breasts, Genitals or Anus", meaning that a picture of someone who has (consensually) been caned leaving bruises and raw skin on their buttocks could be adjudged to be of someone who has sustained "severe injury".
Finally the "rape" clause has the same problem in that if it *looks* like rape, it's illegal, no matter that, again, its a staged act between consenting adults.
Consequently what you have is a law where what is or is not illegal is *not* in any way clearly defined, so it's not a case of "how far over 30mph you are" it's a case of "Yes, M'lud the defendant was, in my personal and entirely subjective opinion, driving too fast, so he's guilty."
PS You're right that it's not rocket science. Rocket science deals in precise statements and accurate measurements, not "how fast do we need the rocket to go?" "I don't know, let's just see what happens when we try to launch it..."