While even a notion of adding the button was often firmly dissmissed, it was always dismissed on "I see the game as X" grounds and it all came down to personal preference.
I've personaly always been for a "carebear" button, with the possiblity of switching it on and off. Many reasons for it.
1) There are/were chances to die to a misclick related to browsers. You could theoreticaly die without having made any rash/wrong decision. This was a major annoyance, infintely more so on endurance runs.
2) Being able to die to a misclick / misclaculation / combat prediction mech screwup adds a manual dexterity hazard to a game which is the opposite of a manual dexterity game. It's very annoying to turn based guys. Funny to hear this from a moba vet, I know, but if I wanted manual dexterity hazards I'd be playing mobas.
3) It affects the learning curve / affinity develompent allready. Two enirely different schools of thought developed around CYDSTEPP directly related to it. One school thinks of Death Protection as "Missclick protection" and prefers strats which invlove it because having a DP on at all times prevents deaths by missclicks. The other, which inludes myself, avoids CYDSTEPP like a plague because over-reliance on having a DP on at all times leads to more deaths by misclick in case you forget to use CYDSTEPP while spiking, or simply click with the mouse before you hit the CYDSTEPP hotkey (and this is also why I use the mouse to fireball stuff and avoid hotkeys in general).
4) Since you cant click on the monster to see the combat prediction at all times, it also creates times when you accidentally miscalculate.
On the other hand, frustration is a big part of wanting to get better at the game, but it's the only argument in favour of leaving it the way it is. I personaly think it's a sneaky skinnerbox gimmick which annoys me despite all the benefits, but I'm not a game disigner, so what the hell...
EDIT: Oh, and misclicks are basicaly the only balancing to the Warlord