This topic ALWAYS chokes me up.
The topic of the “passive” suicide was covered in a wonderful story by Stephen King. I blubber like a “little girl” every time I read it. Check it out in Skeleton Crew or Night Shift, I can’t remember which and the bokos are at my other “home” 
SPOOJE! YES!!
Suicide is illegal because it would be a shitty stance for the government to take that death is a good thing. It would seem that the government, as a regulating body, should not take a pro-death stance no matter what, other than, “It is unfortunate but…”
However, they need not make it illegal. I think we can construct a law in theory with huge practical loopholes.