99% of the comments about this story online think that they're talking about making one NOW. They don't think they can do it now. They're starting initial research into a few isolated systems required to do it one day in the future when materials science and all the other aspects catch up.
It will take decades of R&D, but someone might as well start on the bits we can do now, like a system for climbing the tether (which this is, and it's being done purely in space).
The base tether point would need to be far away from anything! In the book Red Mars by Kim Stanley Robinson, one is placed in Trinidad and Tobago.
The most dangerous part would be slowly dropping the cable; lower it to the point where it could be pulled into a magnetic clamp -- without destroying everything in its path.
It will take decades of R&D, but someone might as well start on the bits we can do now, like a system for climbing the tether (which this is, and it's being done purely in space).