No matter which side of the argument you are coming from, the truth is euthanasia is the killing of a life. Simply put, even if the intent is not the same, euthanasia is still the murder of a human being.
Many would argue that all life should be cherished no matter how big or insignificant they are. With that point being made patients who consider euthanasia are throwing their valuable lives away.
Another problem that arises is when a patient is considered a “vegetable”. How can a patient who can no longer contact the physical world give consent to perform euthanasia on them. There has been various cases (Netherlands) of relatives giving consent to perform euthanasia in order to get to the will that the patient will leave behind.
As a final note, the not everyone is willing to perform euthanasia on a dying patient not even their relatives.