Yes, a doctor should be able to take a live person's organs to save another person's life should happen under very specific circumstances. The person would need to consent, or if declared incompetent, then their Power of Attorney would need to consent. As long as consent if obtained, I do not see anything wrong with this.
I think it's ok to take a live person's organs to save another person's life. As long as the living person agrees, I don't see why it's a problem. It's an issue of helping the greater good. Organ donation is always a good thing regardless of whether the donor is living or deceased.
If it is possible for an individual person to donate part of his organ, or in the case of kidneys one of two, then it should be applauded and commended. This often takes place when family members are an adequate match with someone who needs an organ transplant, and it is the ultimate act of humanism.
Such as a kidney, I am assuming you mean? Yes I think it is fine as long as it is safe. I understand, unfortunately, that once in a while things go wrong, such as the person who recently passed away whil donating a kidney. But I think the practice should go on.