"our boys have no defence over Germany".
Quite, but they can outrun every nightfighter in the sky and turrets don't help much against anti aircraft guns.
but no-one in a position of authority at the time would have instructed Avro et al to build twin engined bombers with no defensive weapons instead of four engined aircraft bristling with machine guns, in case the decision was wrong.
Perhaps, but there would have been little cost to removing all the turrets from one squadron of Lancs, and then see how they got on. That is what the OR boys wanted. Moreover, this was not hindsight but a conclusion made at the time but not passed to Harris.
As far as I can recall no one suggested an entire bomber force composed of Mosquitoes. (I don't see a Mosquito carrying a Grand Slam, for examle.) The suggestion was to strip the turrets out of the 4 engined bomber force.
Of course, if all the numerous RF transmitters that the RAF habitually flew to Germany with - making them easy prey for even none-AI equipped nightfighters that were fitted with RF homers, were removed or turned off, then, so much the better.