I see that asteroid mining had already been extensively discussed in the context of today's technology (Ex. Is Asteroid Harvesting economic?) and the answer is a definitive "No" - it's not economical from Earth's perspective.
But what about the future? Assuming that a number of technologies would see a breakthrough, would it make sense one day to bring materials from space back to Earth? Let's presume that we have at least the following:
Space elevator. Anything, including ISS-sized crafts can be lifted to geostationary orbit for a pure energy cost, and the energy can be effectively recouped when we lower the cargo down to Earth;
Nuclear fusion. We can equip our space facilities with energy supply that is orders of magnitude higher than today and not depend on massive arrays of solar panels;
Advanced robotics. All mining facilities and cargo ships can be operated by the AI;
Do you think it would make sense to mine the asteroids and bring the materials back to Earth in 100-200 years?
P.S. There are also some assumptions for this scenario:
Nuclear transmutation is still not economically viable in this time period;
Manufactured products are still in great (and growing) demand on Earth. We can either be bringing raw materials, or refine them in space, or build whole consumer products in space and lower them down, whatever is more economical.