Nope, you're wrong. Assumptions can save your life. It is natural and instinctive to assume. We wouldn't have made it past the stone age if it weren't for our ability of assumption.
Let's say you were a tribal person living in Africa and you see some fearsome looking strangers from another tribe coming with spears in their hands. Would you assume that they are coming to kill you and your people and take defensive action or would you just kick back and not assume anything until they show you what they want?