As for planes, it's not about the weight of the bottle vs. the weight of the passenger, it's about the energy required to move the bottle vs. the environmental

As for planes, it's not about the weight of the bottle vs. the weight of the passenger, it's about the energy required to move the bottle vs. the environmental impact of how the bottle was made. Small amounts of weight multiplied by many flights equals lots of fuel. American Airlines once saved $40k/year in fuel by taking out a single olive from each of the salads it served. We don't just bury our trash, that's an oversimplification. Modern landfills are designed to prevent leachate (water that soaks through the landfill) from entering the water supply. Putting something in a landfill is one of the best ways we have to safely store it. Contrast that to dumping plastic in the ocean or remelting it without adequate exhaust gas cleaning and land-filling plastic looks really nice. I'm not saying plastic pollution isn't a problem. It is. But landfills are a good solution.