What are the Rules of Scavenging at a Landfill?

We have been rehabilitating a 100+ year old house, and that experience has taken us to our local landfill on more than one occasion. The visits have had two objectives. The first has been getting rid of things that cannot be salvaged. We pulled all the wood lathe out of the bulging walls that we replaced with dry wall, but the plaster had to go. The other is that there is a salvage place at the landfill that sells doors and flooring and fixtures and stairs that have been salvaged from old homes that are being torn down. We have put age-appropriate molding in around rooms that lacked it. We have put flooring into rooms that did not have it. And when we wanted to put a large closet into an upstairs bedroom, we wanted to put molding that matched around it. So we are great fans of re-using.
Today on a trip to the landfill, my husband was yelled at for foraging.
"Hey, you can't do that!"
"Why not?"
"People put their stuff in a landfill because that's where they wanted it."
Is that true? Do people really elect a burial place for their things? For myself, I feel like it is the only choice left to me, rather than feeling strongly my stuff should be there. And does that matter? As a society, shouldn't we encourage reuse? Scavenging serves the greater good. It allows for less waste, and broader use of things. I believe that within several decades, we will be digging up landfills and looking for things in them--natural resources that were once so plentiful they were buried will become rare, and landfills will become the new gold mine.