No one needs a gun. Owning a gun is an individual decision. Some people have emotional issues with guns and have decided to not own one no matter what. They're adults and that's their decision. So you don't
need a gun.
So how do you decide if you should get one or not? My personal belief, motivated by my spiritual beliefs, is that all non-criminal adults, by default, should own a gun, unless they can find reasons not to. There are many possible reasons not to: you hate guns, you don't have the money for the gun and training, you have children around and don't trust yourself to secure it properly, your living situation is such that it can't be properly secured, you are prone to depression (or other emotional or mental factors), it's not legal for you to own a gun, or you just find guns so boring that you wouldn't invest the time needed to learn it. That list of reasons not to own a gun is not exhaustive; there could be many more. But, in my opinion, driven by my spiritual beliefs, if you can't come up with good reasons not to, you should.
Guns vs. taser: There really is no comparison here. Tasers are basically for law enforcement officers who have laws protecting them from liability, and have liability lawyers and insurance and the city to back them up. Non-cops just don't have any good scenarios for using these kind of "non-lethal" force things. Tasers are dangerous and can kill someone with heart conditions. They need training just like a gun needs training. They are probably more expensive than a basic gun. And all this is aside from the fact that guns are much much more effective. I think non-law-enforcement civilians should stay away from tasers. Pepper spray is another one; it's safe and non-lethal, but it's not nearly as effective as a gun, not even in the same ballpark. It's good to have pepper spray but it is not a substitute for a gun.
Basically, if your life is not in danger, then you don't need any kind of force. If your life is in danger, then you are justified in using lethal force. There isn't an in-between situation for civilians. Cops do run into the in-between situations and so that's why they have tasers, batons, etc.
The other advantage of guns is that guns are FUN. It's fun to learn a new skill. It's fun to shoot. It's fun to try out different kinds of guns and pick the one (or more than one) you want.
And finally, by owning a gun, you are exercising one of our fundamental rights. The way to keep that right is to exercise it. We should all do it if we can.
Getting started with a gun does not have to be expensive or difficult. The first thing to do is to really ask yourself "under which situations could I use deadly force? Am I prepared to do that? Am I prepared for the consequences? Do I trust myself with this? When is lethal force justified and correct?" To answer those questions you need to do some thinking, some reading and some talking. Talk to your spiritual or moral advisor, talk to a lawyer, talk to friends you trust and figure these things out.
The second thing you should do is find someone near you, preferably a friend, who has plenty of experience with firearms, and can help you get started. Try going to the range and testing out a few different firearms to see if you like it. It seems like every range has some classes (of varying quality) in the basics of gun safety, basic use of firearms, and basic self defense with a firearm. Some of these range classes are good, some are not, but they are a good place to start. Take one of those classes, or several of them.
Finally, after having done some reading, taken some classes, talked to whoever you should talk to about it, you'll be ready to buy a gun. Which kind you get is up to you. They'e all effective, but some are more effective than others in some situations. It's most important to choose one that you like, feel comfortable with, and will practice with. For indoor use in your home, a handgun or perhaps a shotgun is best. Shotguns have much more stopping-power but are also more difficult to use and more intimidating (at both ends!). So a handgun is often the best one for home defense.
Handguns don't have to be expensive. You can get a fairly good new revolver such as a Taurus in 357 magnum for about $300. This would be a good choice to start with. You could also get a used Smith and Wesson or other higher quality revolver in that same price range, if you have someone who can help you pick a good one. A 357 magnum revolver is probably the best way to start, because they are so simple to use, and reliable, and you can see how they work just by looking at them. 357 magnum is a powerful and very effective cartridge, but one other cool thing about 357 magnum revolvers is that they can also use 38 special ammunition. 38 special is effective enough, and has less recoil so it might be more comfortable to use.
If you want to go for a semi-auto, there are plenty of choices there, too. You can get a Glock for about $500. They are very effective and simple to use. I like them. But automatics do have more buttons and moving parts and complexity so starting with a revolver might be better. It just depends on how much training you want to get.
So, if you go for the inexpensive revolver, you'll spend $300 on the gun and about $500 to $1000 on training and practice ammo. An auto such as a Glock will be $500 to start with, and of course there are autos costing many times that if you want to spend it.
Finally, I strongly recommend getting several days of real professional training. I have taken many many classes at Front Sight (
http://www.frontsight.com) and I would recommend at least a two-day class there. You will learn a lot about it and you will come out ready to use your handgun (or shotgun) to defend yourself. There are several other schools too, but I only have experience with Front Sight.
One other site which will help you make your decision and give you some good links is this one:
http://www.a-human-right.com. Read through it and think about it.
Think, think about ethics, think about safety, and then decide.
One more important thing to keep in mind is that all of this can be FUN. The training is fun, shooting is fun, you'll meet fun and friendly people, it's a fun activity to do with friends, etc. If it weren't fun I wouldn't do it, myself.