How important is it? Should someone be free to make choices that would surely result in harm nor even their demise?
This is a really good question and I want to express my view without going into too much theoretical details.
Free will is, IMO, one of the most important thing in anyone's life. Our "free will", or in other words, our ability to make decisions, allows us able to make "good" and "bad" decisions. Now you might think that if a person is allowed to make bad decisions like you say, then it is not "good", because it would hurt the person himself/herself and other people.
But what if, no one is allowed to make "bad" decision that will surely hurt oneself/others? Can you imagine how the world would be?
You might think, oh come on, there could be nothing wrong, right? Everyone will live in peace and harmony, since there will be much less wrongdoings in the world.
You are right. There will be much less lawless things in the world, but it comes with a cost: love will decline in this world as well.
Why? Because the depth of love cannot be extended any further if there is no harming in this world. We cannot love a person deeply when he/she could not hurt/be hurt all the time, because he/she requires no mental needs (or I would say spiritual needs). Love will become superficial that we will only help other people's physical needs.
For example, if a man is in depression, but never in risk of hurting himself, will we be worried about him? Maybe, but probably not that much. But if he could choose to hurt himself or even suicide, we will have a much greater desire to help him to get over it.
If a man is always angry, but is never allowed to shout at or hurt others, will we even care about him? Probably not. But if he is allowed to, we would find ways to bring calmness to him, in hope that he would not be a person who brings uncomfort and danger to others. The depth of love cannot be seen and experienced when people cannot harm themselves/others.
Let's go back to the real world. Is it then a good thing to harm others/ourselves, so that people can have a deeper love to others? No, because it is a bad thing for the offender. It makes him a person cannot love. He would not find the joy and satisfaction to love others.
IMO, God has put us in this wicked world, for a purpose that we could truly love one another, and choose not to harm. And He will choose the ones who can love one another as oneself to enter the kingdom of Him. People in this kingdom will therefore know how to love deeply. I can assure you, that this kingdom will be a better place than a kingdom in which people can never choose harm.