This is such a difficult topic. It's purely a personal opinion, but I think that both the doctor and the system were right. But instead of suspending his license (and losing the services of a skilled doctor), a more appropriate punishment would have been for him to be obligated to give a percentage of his wages to a cancer research charity for the next 5-10 years.
This is a debate we've been having in the UK recently, with the government pushing through an "Assisted Dying Bill". It is intended to allow doctors to provide caring euthanasia to relieve the suffering of terminal patients who ask for it.
But there are major concerns. What if a greedy relative has power of attorney and persuades a doctor to do it in order to get an inheritance ? What if a doctor makes the decision unilaterally, as already happens with the "Cambridge Pathway" currently in use - there's a scandal brewing on that, where doctors have been reportedly assessing patient's cognitive ability (a key part of making the decision on whether to put them on the pathway) after administering strong sedatives. More importantly, with the government clearly seeing pensioners as a cost to be reduced by any means possible (including increased taxes and removal of the Winter Fuel Allowance), how long before "right to die" becomes "obligation to die" ?