[beAbU]

At some point a massive landfill will become more economically viable to mine for rare or useful elements than an actual mine. There is a good case for piling rubbish into to a well-managed landfill for future generations to mine with better technologies.

Also, burning plastic waste in a power plant at least liberates the energy for use. One can argue it's just fossil fuels that spent time doing something useful before it became energy.

Taking rare elements to space only for it to stay up there or burn up in the atmosphere removes it from this whole equation.