That's not how the law works. That's essentially saying if no one tells you not to, you're allowed to.
Not all persons seeking access to property are trespassers. The law recognizes the rights of persons given express permission to be on the property ("invitees") and persons who have a legal right to be on the property ("licensees") not to be treated as trespassers; for example, a meter reader on the property to read the meter.
You aren't a trespasser if you walk into the McDonald's to order food, you're invited to. You are not invited to climb on the roof.