It's that people might use a toy emoji which others interpret differently.
These two messages would be interpreted very differently:
> I'm going to get you back. :toy_gun:
> I'm going to get you back. :real_gun:
Secondly, you're entirely missing the point of my comparison. I have never used the real gun emoji, but I might certainly use a toy gun in fun. The problem is that the composer might be trying to send a fun message, but it would be received negatively.
To be clear, I really don't care either way about the existence of a gun emoji. If Apple wants to remove it from the keyboard, that's fine and if they want to keep it that's also fine by me. My concern is with silently introducing a non-compatible change: it's analogous to silently making a dramatic change to the side effects of an API method without changing the name or announcing the change.
Why are you so defensive of this move? What advantage is served by switching out the emoji instead of simply removing it form the keyword?
Do you think this emoji exists on the Apple keyboard without ever being used?
Is there a class of people that you're both (a) comfortable enough joking about shooting with toy guns, yet also (b) slightly nervous about them coming after you with a real gun?
Maybe you played a prank on your boyfriend. It's entirely possible that he would get you back by shooting a water gun at you. But it's also possible that he might get really mad about it and threaten you.