Peter--lot's of things can be changed by peer pressure. Like for instance, smoking. Kids use peer pressure to get other kids to smoke right?So we should make it illegal so they can't do that anymore?
When it comes down to it, it is your choice. An old women isn't just going to give up her life because her son tells her too. Granted, if the son made her hate her life to a point, I would call that harassment, and have THAT against the law. But as far as telling her that it is going to be painful, hard, and pointless... that's not going to FORCE her to make the decision, it will help her make it, by realizing what the natural death will be like.
Just as the first cigarette you smoke, if your friends are forcing you to smoke by surrounding you and shoving it in your face, that can be called harassment, and is illegal. But if they tell you it's fun, it is YOUR choice to try it. They helped you make the decision, but they can't be blamed. You made it.
You can't prevent everything from happening by taking away rights, because that is unconstitutional. And it won't work anyways.
The mother's son will have her son kill her, probably sending her son to prison on man slaughter charges for a few years in the process.
The teenager will still try smoking, get addicted, and end up in jail for illegal tobacco use.