There’s an interlock that turns of the magnetron when the door is opened. If the interlock failed, you could get burned it you opened the door and got exposed to a full blast of microwaves. Still, I trust the interlock and do what you did all the time.
I would be inclined to agree with you rather than your friend. Microwaves do not make your food “radioactive”; they just make it hot. Microwaves are “non-ionizing” radiation.
Of course, if the oven is damaged in such a way that it continues to work with the door open, there’s always a risk of you being “made hot” and getting burned (and then this happens). But again, that’s a highly unlikely malfunction.
Even if we removed the off button on the door, it still wouldnt “let out dangerous radiation” or whatever nonsense your friend beileves. Microwaves generate -you guessed it- microwaves that excite water molecules so food gets warm. There’s no mysterious radioactive gas like in some Troma movie. The door is there so you dont get burned, just like your oven door.
Dangerous radiation is typically ionizing radiation which is stuff like xrays. You dont own anything that makes dangerous amounts of xrays.
on devices with a mechanical timer the timer will still run after you shut the microwaves off by the off button or the door open button (which shuts off the microwaves if the interlock is working).
If the interlock did fail, how bad would it be to be hit with microwaves from a typical microwave oven for a few seconds? Presumably, if this happened, you’d notice that the microwave was still on and hit the off button a second or two later. Would it make a difference if you were wearing metal (watch, jewelry, buttons, etc) or not?
the microwaves in the oven cavity no longer exist to stray anywhere before the door opens if the interlock is operating correctly (if the fan, light and carousel motor shut off then so do the microwaves).