I agree that in a weapon retention situation, if your pistol has a magazine disconnect safety (MDS) and you feel you may lose control of it to the BG struggling with you, hitting the magazine release and dumping the magazine will make the gun safe and may prevent you getting shot. However, I've always thought that any moderately knowledgeable BG would simply bend down, pick up the magazine, insert it, and...
My big beef with a MDS is that if I've had to use my pistol the hard way, and am now holding the surviving BG's at gunpoint, I want the weapon to be in firing condition at all times. I'm probably going to reload, so as to have a fully-charged weapon. If the pistol is rendered inoperative during the magazine change, even if only for a second or two, according to Murphy's Law, that's when the BG's will try something! No, thank you very much, I will not own a pistol with a MDS...
I'm a bit annoyed about this because it removes some really nice pistols from my inventory (e.g. Browning Hi-Power, all the Smiths, etc.). Yes, they can be modified to remove the MDS, but if one removes a "safety" feature from a weapon and then uses it in self-defence, you can be sure that Ima Shark, ambulance-chaser, will use that fact against you in court when he sues on behalf of the family of the late Joe Scumbag, BG. "But, ladies and gentlemen of the jury, he DISABLED A SAFETY MECHANISM ON HIS GUN! Just the sort of thing an evil-minded Rambo-type like this would do... make it easier for him to kill poor, innocent muggers like the late Mr. Scumbag! Don't let his evil behavior go unpunished!" Yeah, yeah...
I can do without that hassle, thank you very much!