Not if they collide with Earth We need to capture them and if we can't mine them right away at least put them into convenient orbits. This can be done already, we have the tech. The economic question is still open, however, until actual mining begins. I have numbers for the economic question; mining can be done as far as business is concerned.
By far the biggest obstacle to technology is LAWYERS! That's my worst fear...liability lawsuits in space...I feel an entire fresh ad hoc legal system would be a great draw to get people up to space and also give the economic impetus to do risky operations like asteroid mining...But it would amount to secession(sp?) from the Earthly economy to be protected from lawsuits...Tough issue...Wish I could be frozen for 200 years...But I've got reasons to stay "warm"...and sci fi covers all eventualities...