I agree the suggestion of simply unmapping quick load is the way to go.
From a interface perspective, you are asking for every single player to have to do 2 button presses instead of 1 to perform the quick load function. Hit F9, then confirm. And it is not even guaranteed to prevent the problem you are having. If people most of the time just want to quick load, and the confirm yes is just an other press of a button, you can still get into the habit of hitting F9 and then hitting the button automatically (since that is what you want the vast majority of the time), and be annoyed at the extra step the game is making you take. And then when you didn't mean it, get annoyed you clicked confirm too fast.
However, the option you've mentioned, unmapping, is currently 4 actions along with picking which file you want. Esc to menu, press load, press file have the option of doubling the actions one needs to take to "quick load" (i.e. 2 button presses instead of 1) for everyone, or for the people it impacts, you can go from 1 button to 3. Esc to menu, pick load, pick top save, press load (4 button presses). I feel this is much better and more likely to make you think about what you're doing since you have to pick the file you want.
Its only a factor of 2 in terms of additional steps from what you're requesting, as well as already having been implemented, so no development time necessary.
The other option is to play ironman.
