I'm all in favor of finding a business reason explore the solar system, but I'm not sure that we have the technology to make asteroid mining profitable.
There are over 1,500 asteroids that are as easy to get to as the surface of the Moon. They are also in Earth-like orbits with small gravity fields, making them easier to approach and depart.
Asteroid resources have some unique characteristics that make them especially attractive. Unlike Earth, where heavier metals are close to the core, metals in asteroids are distributed throughout their body, making them easier to extract.
Asteroids contain valuable and useful materials like iron, nickel, water, and rare platinum group metals, often in significantly higher concentration than found in mines on Earth.
I'm not a geologist, but don't vulcanism and water play an important role in concentrating metals on earth into veins that can be mined? If these valuable materials are in an asteroid wouldn't they be distributed rather uniformly? How would they be separated from the rest of the rock?
For comparison, there's a lot of gold in seawater right here on earth. Water and gold are pretty easy to separate, but no one has yet found a way to make a profit doing this. Wouldn't it be exponentially more expensive to separate platinum from rock on an asteroid?