I think people hurt other people for no apparent reason at all because they are not happy with their life and they are taking it on others. Somebody did that to me and after all the embarrassment she caused me, she said she was just joking. They have no accountability for what they are doing to others. I think they are secretly envious of the person they are hitting.
Our society is a melting pot of differences. Usually when someone, (Not known to be a joker of sorts) make hurtful statements it is a sign that they are unhappy and don't wish happiness for others. There is also a mental condition that may aid in the uttering. Some are just plain nasty for no reason. In a few cases, they may be lacking some chemical they need in their body that affects their actions.
I must agree with insecurity of others will make them verbally attack others and even when they find out the truth of their abuse, they are still to shallow to apologize, but that is the way of some people and I chalk it up as their own personal problem and they have to live unhappy with their issues.
Because they are insecure themselves I think. And I think maybe it makes them feel superior...or maybe they have something wrong with there minds.LOL
I'm sure there's as many reasons as there are mean people. But it usually comes from, in my opinion, fear, pain or ignorance. Remove those negative things and happiness is much easier to achieve ;)