I don't know if it is right or wrong, and I realise this is a sensitive issue, but I feel that it should be legalized.
Any of us who have seen someone suffer through a prolonged and painful death would see how pointless that suffering can be. I think it would be difficult to find anyone who would let their sick dog or family pet go through that.
Euthanasia absolutely would open a huge can-of-worms (for instance relatives trying to a hold of the inheritance) but this is no excuse not to go ahead with it. There would need to be a lot of strict conditions in place to avoid abusing the system.
I also would agree that it is not for everybody. Individual beliefs, religious or otherwise, should always be respected.
It is widely known that this kind of thing already happens, so maybe it is about time to bring it into the open.