I think like Shirley said it depends on the situation. I can say that my grandmother went on life support back in 2006 I believe. I think I was 11 or 12 and although she was only on it for I think around four maybe five days I can say it was extremely hard for me and my father especially. Only reason my father kept her on life support was because the doctors had said she had around 80% chance of coming off of it. I know my father said if there was even just a 50% chance he would have. Anyways she came off of it and lived another three years. She passed away back in 2009 after going on life support again. Her chances this time had drastically dropped to around 20% I think. Sorry for me being vague, but I try to remember the good times I have had rather than the bad. I also am not good with dates.
Let me ask you this and I would like to say I don't mean it in a disrespectful way, but have you been put into the situation where you are in control of the life of another human being and not just any other person, but your own mother? father? son? daughter? brother? sister? No one wants to lose their family or friends and I think when we have them on life support it is not because we are trying to be God, but rather we aren't ready for life without that person. When it comes to death we are all just children. We can not control our emotions. Although as Christians if we knew the person was a Christian then we know they will be in Heaven. However, even with us knowing that you would think death would be easier for us and it isn't. I don't know one person who can handle death.