The great writer and adventurer Ernest Hemingway once wrote, "the world is a fine place and worth the fighting for." The quote which is from For Whom the Bell Tolls by the way is how most people seem to see the world, but there are always acceptations.
Like you most people strive to make the world better and fight in their own way to improve things and share their views with others. Most people can be reasoned with and things can be worked out eventually even if things are a little rocky, but what do you do when talking isn't an option. There are some people in this world who don't want to peacefully coexist and will think nothing of taking your property or your life. When confronted by evil or rage you can try and take the "high road" or you can fight and survive.
With enough time and patience you can teach anyone the fundamentals of self defense, but it is meaningless if they don't have the right mindset. You can't make someone brave or aggressive they have to develop these feelings on their own, but training can make them more confident in their abilities and that foster those feelings. While learning hand to hand combat isn't easy and there will be some mistakes and bruises along the way, but it the will to fight and defend yourself and others that is most important.
Now perhaps you know someone that is disgusted by needless violence and sees every man as their friend. These are great ideals, but not all violence is needless and not everyone wants to be your friend. You should try and get along with your fellow man and violence should be your last resort, but when you're forced to go that route don't come up short. If you're trained you can make the violence end faster and prevent others from getting hurt.
When you look at warrior cultures often times you find they developed not for conquest, but for self protection. For the knights of Europe and the samurai of Japan and many other groups it was about protecting home and family and if they were going to do that they needed to be the best warriors. The fact is if you're a good warrior you can choose which path you go down, but if you don't fight back others will choose for you and it will be to their benefit.
If you want to keep your part of the world safe you have to be willing and able to fight for it when the time comes. There are horrible people who walk this earth who kill and take what they want until someone stops them and they see your value system as a weakness. You don't have to be out looking for a fight for a fight to come to you, so be ready so you can make it home safe. If you ever question why you train remember all the wonderful things you have in your life, because someone will take them all away if you don't fight back.