There are some good comments and cautions in this thread, and a few bits of... much less useful information.

Personally, I'm in the Muss Muggins camp of having a few favorite handguns in rotation. I vary them depending on the weather, on what I'm wearing and just on my mood at the moment.

I'll give a nod to folks that indicate there is some advantage in carrying the same gun, in the same holster all the time, but there is a lot more involved than just using the same handgun all the time.

The bottom line is that you need adequate training and proficiency with any handgun, but that doesn't have to limit you to just one. Additionally, there is also often some directionality in the conversion process from one handgun to another.

If you're going to carry a handgun you need to practice and shoot with it enough to be able to effectively employ it, and more importantly be proficient enough be able to do so under extreme stress, which requires the actions to be second nature and automatic.

However, once you've truly mastered a specific handgun it may not take much to adapt to another similar handgun. For example, if you are proficient with a 1911, you'll find a Hi Power isn't significantly different in terms of controls and operation. You'll also find that a CZ 75B or CZ 75 Compact isn't significantly different in SA mode.

Once you've mastered a 1911 or other SA "cocked and locked" semi auto, a DA auto or DA revolver offers only the additional challenge of mastering the longer, heavier DA trigger pull and longer trigger reset.

The reverse however isn't necessarily true. For example, someone proficient with a DA revolver or a striker fired pistol without a manual safety will have to learn to deactivate the manual safety on an SA semi-auto. After all, you can't forget to deactivate a safety that isn't there (going from a 1911 to a DA revolver), but it's much easier to not think about deactivating a manual safety if you've moving from a striker fired pistol or DA revolver to a manual safety equipped SA semi-auto.

Fit matters as well. The 1911, BHP and CZ 75 also have similarities in the grip - if a 1911 fits you well, a Hi Power and a CZ 75 should also work well for you. I've found however that an M9 or similar Beretta 92 is just too large in the grip for me to control as well as a 1911.

Similarly, most 9mm Glocks feel like way too blockish in my hand, and I absolutely hate the triggers on most of them. The end result is that while I shoot them better than many people, I don't shoot them nearly as well as a 1911 when it comes to controlled pairs, double taps, or failure to stop drills. For that matter I don't shoot a Glock as well as I shoot a K or L frame revolver, and it's mostly a matter of fit.

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The bottom line is that if you're not going to devote much time to developing and maintaining a high level of proficiency, then yes, you are probably better off with just one self defense handgun, focusing that limited (and probably inadequate) practice time on just a single handgun.

But, if you are a gun person who likes to shoot, shoots a lot, and you're willing to put in the necessary practice, there's nothing that prevents you from being fully proficient in multiple handgun types.