I support it. If an animal is suffering, you put it to sleep. Why do we make humans go through the suffering, for years sometimes?
One of my grandfathers had a long battle with lung cancer. He suffered for a long time [[several years). At 6 foot tall, he was around 90 pounds when he died. One of my grandmothers also fought cancer. Her battle was less than a year, but the cancer kept spreading. It eventually moved to her brain. Not only was she in pain, but she was blind for the last few weeks of her life and she was not aware of anything.
If you are terminally ill and suffering, I think it is the humane thing to do.