" Oh, I'm pretty sure I'd rather wrestle a handgun, or especially a rife, out from a persons hands than a knife. I wouldn't get cut that way."
If someone levels a gun straight at you and its clear they wont hesitate to use it how quickly do you think you can move yourself out of its path and trap their arm compared to their squeezing the trigger at the first sign of trouble? Whilst you are correct that you could get cut in the struggle, how confident are you that an accidental discharge in the struggle wont wound you just as badly? Once an arm is trapped it becomes a lot more difficult to use a knife but it is still quite easy to fire a gun you are holding.
I dont like those odds one bit. A person holding a knife has to lunge at you with it having gotten reasonably within reach. Timing wise you are more evenly matched.
Also, unless they are an expert knife thrower you are more likely to get away safely too.