So if gold plated fake hand grenades are to be allowed without a fuss, does this mean a real hand grenade that is covered in the gold spray paint should be allowed? How is a TSA screener supposed to tell?

There's a reason why a fake weapon is barred if it is not "obvious" it is fake. The reason is that if a victim airside is convinced it is fake, it can be used to hijack a plane.

I am not seeing the logic of those arguing against the OP in this situation.