Again, different opinions on this subject.
You say that no instructor rating is required to teach aerobatics etc, yet an instructor requires the no aerobatics restriction removed before teaching.
You could demonstrate eg a loop or roll to me which I could watch as a passenger, the problem is if you let me " have a go" and i enter eg a tailslide and break the rudder.
Though it might be common to let friends have a go at flying the plane, somewhere in the ANO ( sorry I dont have it at hand to find ref) it forbids the captain from allowing anyone else to manipulate the controls (single crew plane) unless they hold an instructor rating or agree to relinquish command to another qualified pilot. This I see as the legal problem with " check outs" carried out by PPLs?