Maybe it's different in Korea, but in the US, patients absolutely have the right to refuse life-saving measures. I work with cancer patients and they are allowed to deny treatment if they want to. Obviously, you shouldn't ask some random person to turn off your life support, but if you tell your doctor you don't want to continue with treatment, they will have a thorough discussion with you to make sure you know the risks/consequences of stopping treatment, but they will still respect your wishes.
Maybe it's different in Korea, but in the US, patients absolutely have the right to refuse life-saving measures. I work with cancer patients and they are allowed to deny treatment if they want to. Obviously, you shouldn't ask some random person to turn off your life support, but if you tell your doctor you don't want to continue with treatment, they will have a thorough discussion with you to make sure you know the risks/consequences of stopping treatment, but they will still respect your wishes.