He chose to supplant God's will with his own will. The suffering that results from sin was not caused by God. It is a part of the package deal that Satan offered. Man bought it, lock, stock, and barrel. One can choose to be and to do what he pleases, but he cannot choose the consequences.
Death is the built-in ultimate consequence of sin.
The very fact that man is conscious of his failure and is aware of his sin is proof that he is not a mere animal. Neither a one-celled being in primordial ooze nor the most advanced primate in a zoo ever questions why he was so made. Only one creature bears the image of his Creator and can probe the purpose of his creation. Sin never was affirmed of animals. The very fact of sin in the universe proves that man is more than an animal.