Hey,
indeed i not really understand your argumentation.
You say: telling beginners the exact position of suspects is not spoiling the game for them, but ordering a grenade does?
I'd rather say exactly that is a main reason for EXPERIENCED players not using the opti: you spoil the game and nullify the (awesome) randomization system of the game.
Of course i know ROUGHLY what to expect in a room (cause i know the maps). BUT using an opti i know EXACTLY what is going on.
That takes away a lot of the challenge.
I never denied using an opti is a pretty safe way and very suitable for beginners (but then they have to use it themselves). That also was not my point! I'd NOT say "never use it".
There are good arguments for and against the use of the mirror device.
But its excessive use at every door is simply spoiling the game for everyone and slows down gameplay (which takes away immersion) - in my oppinion!
Greetings