seems like a lot of people think compromising the vacuum could lead to train derailment and very likely the death of everyone on board (they're traveling at 700 mph after all)
It's far less at-risk if it's in a tunnel under the ground.
Actually, tunnels are riskier than at-grade. A fire in a tunnel is basically a deathtrap, and can even seriously impact people not inside the tunnel (see https://en.wikipedia.org/wiki/Howard_Street_Tunnel_fire for an example of the latter).