If a proper weapon, a shotgun, is used it's also a different situation. Shot won't travel through walls and put your neighbors' lives in danger. The nature of a shotgun doesn't require much of the user than to point the weapon in the correct general location and pull the trigger.
You do have to keep in mind your environment when choosing a weapon and ammunition, as the two work together. There are many good choices besides shotguns, and in fact some are better than shotguns even if you live in a confined space like an apartment. Look up frangible ammunition or penetration studies of different types of guns/ammo. Even American air Marshalls carrying firearms on planes choose pistols, but choose frangible ammo.
No one has said a peep about this: but tactically concealing weapons only ensures you can't get to it fast enough should you need it anyway. The type of person that feels safe because of a gun is exactly the kind of person that shouldn't be carrying it.
Tactically concealing a weapon ensures nothing of the kind, else plain clothes detectives and federal agents wouldn't do it. There are many ways to carry a weapon, some faster to access to others, but ALL of them are faster than running back home to get your gun or calling the police and waiting for them to arrive.
What you reference is one of the big anti-gun/anti-ccw straw man arguments, that every encounter with a potential attacker is a "quick draw" situation and you either have to draw and fire on a second's notice or it's all over too quick to respond. This is simply not true. Many violent situations develop over a period of time, they often involve people you know to be a threat so you see them coming, and the gun may empower you to get involved to help out someone else facing a dangerous situation. bottom line is ... a lot of people have had things happen they would have liked to have had a gun available to deal with (read the papers) concealed or not.
The bottom line is ... training for simple self defense is easy, carrying a gun is easy and legal in most of the United States, you do carry it with a round in the chamber, and while it's not a cure-all for every situation ... it's an option and an empowerment, and having options is always better than not having options. And that's the bloody truth mate.
And I'm also curious as to where you hail from ... you use language that sounds non-American, but you claim the viewpoint of a police officer who has experienced people carrying concealed weapons. As far as I know the legal carrying of concealed weapons by civilians is pretty limited in most countries (not all are as dedicated to liberty as we are) besides the US.
When you think about the empowerment of having the option of carrying a weapon if the need arises ... who wouldn't pursue that, even if they didn't want to actually carry a gun on a daily basis? If it's available where they live I would think everyone would want to get their license even if they don't plan on using it.