I'm a Buddhist and I believe in Karma.
Unfortunately Karma is a concept which has been diluted and confused in the West and people who use the word, don't really understand what it means.
I think it's because most people in the West grow up influenced by Christianity and it's concept of sin and punishment. So they think that Karma is the same thing and that you get punished for being bad - it isn't.
I'm no expert of course but I'll try to explain it this way.
A lot of Buddhists understand Karma in this way. The mind has existed from the beginning of time, a bit like a stream. It passes through life after life. Negative actions you commit result in negative outcomes - somewhere along the stream. Not necessarily in the same lifetime.
So a person can live what appears to be a terrible life doing lots of harm to others and not appear to suffer in that life time. Ultimately however those negative actions will have negative results for them.
Many Buddhists also believe that the ultimate goal of life is to attain enlightenment. On the way to enlightenment a person can achieve a higher rebirth in a level above the human world which helps them on a path to enlightenment.
No real Buddhist believes that people who suffer or are killed in tragic events deserves it, real Buddhists believe in compassion. We believe that everyone is good and pure at the core but that our minds are filled with delusions that confuse us.
Also Buddhists believe that you cannot judge a persons Karma on the basis of their life. For example a person can appear to suffer a great deal throughout their lifespan and die in tragic circumstances and then go on to achieve a wonderful higher rebirth or even enlightenment itself, because in their last life the last of their negative Karma has been eliminated. Yet a person who appears to have a wonderful life can actually still have a lot of negative karma left.
I would ask that people posting in this thread remember that more then 20% of the people on this planet follow a faith that believes in Karma. Disagreement is welcome but please be respectful.