Why not, if the whole point is to test the filters and ethical limits? Asking it for fiction is one of the ways to get forbidden output and to see the guardrails less predictably but strongly assert themselves.
What you're describing is essentially engineering ethos. We find the breaking points of things in order to learn about them and improve them.
Is that not allowed anymore?
Not in a world were the priests have taken over. Then its security by obscurity, aka in god we trust.