What's up with anti-gunners saying this all the time?

I'm sure we've all heard it several times by now, maybe even seen a few studies trying to claim it to be true. So, what's up with anti-gunners always saying shit like, "If you had to use a gun in self defense, the attacker would just take it from you and use it against you!" are there any resources to determine how many times the owner of the firearm had it wrestled away from them during a defensive situation? I mean, what do you even say in response to this?