My dad thinks that I shouldn't trust others so easily and that I am too immatured and naive if I do that...?

What do you think?? Do you agree or not? I told him I disagree with him on that and it makes me feel uncomfortable when I harbor some kind of distrust towards everyone.. but he still insisted to think that way.. I'm way over 18 yrs old btw.. Do you agree with him ? What can I do if I don't agree with him on this. He is dead set on it though..