I think the majority of problems come in when the person is not aware and the family has conflicting opinions, or opinions that some people find unacceptable.
Like when rich old comatose grandma may or may not be in pain and needs expensive treatments that are eating into the inheritance.
There are so many issues that cloud the debate and make it not simple.
For me, if I am awake and decide it's time to go, I'll manage to get it done, no matter what the law.