To let live or die?

Right now the idea of to let live or die is a very hot topic in the news. I have discussed before the hard topic on weather some people should be artifically kept alive or not. I have came to the idea that if a person can understand happyness and sadness then they should be allowed to experiance this. However, if the person can only experiance sadness and pain then I fell it would be more humane to end this circle of suffering. In addition if the person does not have the ability of feeling anything, then he or she must be allowed to exit. For example, a young girl I know, she will never beable to talk, walk, or read. However, she experiances joy and love and brings joy and love. Her parents are happy and there are times she is happy. She should be given every chance under the sky. But a few years back a baby was born lacking a brain. The child had a brain stem therefore grew and did not need outside assistance to obtain air. However, this child could never know what life is, there was no way for the child to obtain the salvation of Jesus or know the love of his/her parents. So why should the parents or child be forced to suffer all the pain in the world without the joy?