Firstly, Missingno. does not crash your game. The only thing it permanently damages is your Hall of Fame entires, which barely matter anyway.
Anyway, Missingno. was not intended to exist, as stated by Nintendo here:
MissingNO is a programming quirk, and not a real part of the game. When you get this, your game can perform strangely, and the graphics will often become scrambled. The MissingNO Pokémon is most often found after you perform the Fight Safari Zone Pokémon trick.
>To fix the scrambled graphics, try releasing the MissingNo Pokémon. If the problem persists, the only solution is to re-start your game. This means erasing your current game and starting a brand new one. - Nintendo
Nintendo wasn't correct about fixing the graphics though, to fix it you have to look at the Pokedex entry of a legit Pokemon. Releasing Missingno. will do nothing.
So basically, Missingno. was unintended glitch in the game. It really wasn't supposed to be anything since it wasn't supposed to be there in the first place.
