Trusting too much?

I've seen a lot of people who, when it comes to anything having to do with people, are extremely paranoid and distrusting. I know how society likes to label them as being overtly negative and their feelings as unnecessary, but, for the most part, can you really blame them? I personally believe that you can only trust a very select few in this life and even then you really have to be careful. People have proven to me numerous times that it is very dangerous to even consider trusting them, no matter how sincere they seem to be. Being too trusting can be best described as naive at best, foolish at worst. And it has cost some people their very lives. So, when I look at that fact in it's entirety, I guess being paranoid is none other than a necessary evil! Trust, in all honesty, has to be earned rather than given.