The problem is that most of the times suicide is not a rational decission taken by someone with terminal cancer to stop their fisical suffering. Most of the times is the reaction of a malfunctioning brain. Most suicidals wouldn't have taken the decission in a normal situation (not depressed) , and those who failed to kill themselves are happy to be alive. That's why it's so important to know the factors that trigger suicide compulsions, and the measures to better fight them.. A depresed person suicide brings a big suffering to the family and friends of the deceased, who most of the times don't know of the intentions.

Suicide is something that can never be fully controlled. It may be illegal to do it, but it's a literal inalienable right, no matter how strong the law against it.