Indeed why are more of the commandments of the whole Torah negative than positive – 365 as against 248?
I once teased out this question with a high school class. “Let’s make the Ten Commandments positive!” I suggested. The class tackled the task but found it extremely difficult.
Instead of “Thou shalt not kill”, the consensus was that we should say, “Thou shalt respect or preserve human life”; instead of “Thou shalt not steal”, the proposal was “Thou shalt honour or protect property”.
All very interesting and very helpful, but far too vague. The advantage of the negative formulation is that it is short and precise.
“Respect or preserve human life” is a magnificent motherhood statement, but it has the drawback of not being very crisp or certain.
I remember what my parents used to tell me when I was a child and we had a wood fire burning to keep the living room warm: “Don’t touch the fire!” – negative, to be sure: but how could they have achieved the same effect with a positive statement?
I am afraid the “Thou shalt nots” are the best formulation we are likely to find.
Bear in mind, too, that when it comes to a real emergency and a person is tempted to act wrongly, a big “No!” is the best way – as they say in Yiddish, Lo mit an alef!, i.e. “Decidedly No!”