My two cents:
Fitst let me start by saying that mistakes can be made. But there is a differnence between a blunder, a legal move that inevitability leads to a loss (unless you are playing me 
). A illegal move is usually govroned by the rules set by the organisation you are playing under. In your case there is no other move to be made and thus illegal, suppose there was one other move possible then under the same rules that move has to be played. Example if you touch your rook first when casteling you have to make a rook move, instead of casteling (which is a king move) then you have an alternative.
1 question for you: You are white and you want to open Nf3. But you touch your bishop. Does this than result in a loss of your game?
In a recent OTB game with long time controls (1H30 + 15s increment) my opponent made an illegal move. In the below position, he played 30... f7-f5.
I stopped the clock and called the referee. According to the rules, he awared me with 2 minutes extra on my clock, and told my opponent to make a different move.
I believe this rule is wrong and the game should have been lost immediately for my opponent, instead.
If there had been a Queen on g8, everyone would have said of my opponent: it's your own fault for making such a silly mistake. It is not right that for a far bigger mistake (leaving your King hanging instead of a Queen), the punishment should be merely symbolic.
I want to repeat that this game was played under long time controls. I accept that the situation in Blitz or Bullet is different. For one, two minutes extra on the clock have some value.
But under longer time controls, there is no excuse for making this type of mistake and it should lead to the immediate loss of the game.