So far, the only justification I have seen for asteroid mining, that can meet the Trillions of dollars needed to set up a reasonable enterprise, are related to rare platinum group minerals. Gold and diamonds just don't cut it!

These minerals have a per-kilo cost that would justify space mining.

Unfortunately, the price is really price-per-gramme, and the economics of successful space mining on the megatonne-scale would cause a multiple-order-of-magnitude collapse in the price (we could all afford rhenium-plated plumbing and rhodium tinsel for the christmas tree).

This vicious cycle of resource price erosion, technological progress, and further price reduction is bankrupting all but the most efficient miners and energy companies, and driving whole countries out of entire resources sectors.

If Space mining became a reality, either it would fail, compared to ground-based efforts, or it would succeed, and all ground-based resource activity would cease in those sectors where space resources were viable.

It wouldn't even be worth recycling things like platinum - we'd just dump them in landfill (they aren't too soluble, so it shouldn't be TOO much of a heavy metal pollution problem)...