So let me get this straight....
If you came upon someone beating the life out of someone on the ground, you could not draw you gun to intervene on behalf of the victims life?
You could only jump in with your hands to stop the 300 pound attacker?
Wouldn't this senario really play out this way? You arrive at the scene of the beating, draw your pistol, and tell the brute to stop. If he goes for a weapon you would then be totally justified to shoot him. He has a weapon and the shoot is clean.
If he does not stop beating the crap out of the guy or starts to come after you, I would then think you would be justified also. Now, a large man with the full knowledge that you are armed, continues to beat the victim or tries to beat you down. I don't know who would not be in fear of their life or the victim's life at this time. If it involved a jury months later I would also think that they would be on your side, even if a overly zealous DA tried to press charges.
Now if you are the guy getting beat silly, and you CC, at some point you should be justified to save your bacon. I would think that at a last resort your defense would be, he tried to take my gun and kill me so I had to use deadly force. As to the guy being able to now use a gun against you if he does and you let him....
If you do CC you should not have let things escalate to the point that you would need to shoot the guy. If it still got to that point then you either take a woopin' or hope your peers show some compassion.