One can represent themselves. It might be dumb, but people should have the right to be dumb when they're the only ones getting hurt. That's why I have no problem with engineering requirements: when a bridge, airplane, whatever falls down and goes boom, it's not only the owner who's affected.
I'm an adult. It's legal for me to buy and drink bleach. It would be very stupid of me to do that, but I can. I should be able to do the same with prescription drugs, if I want to. Yes, including eating a whole bottle of warfarin and dying messily. It's my body and my life, not yours.