Remember when Las Vegas was set to receive the country's first high speed rail between there and LA until Elon Musk promised the city commission that he could do it cheaper using the hyperloop? And then the hyperloop became a murder subway until it eventually crumbled beneath his hubris?
Putting humans in an extremely low atmosphere environment... underground. I let you think of the really bad accidents that could occur from that. I'll start you off with, what if there's a fire? What if there's a leak? Or an earthquake?
It's got all the terror of space, but you've also got thousands of pounds of earth overhead. Makes Oceangate's Titan sub seem downright safe by comparison.