I don't see them as explorers.
People have been going down there in subs for like 37 years. These were just tourists.
I also don't have a problem with them being there because its "a grave". Life is temporary; just because people died there doesn't mean that place is off-limits for all of eternity. I guess its the same reason I dislike cemeteries.
Is it sad these people died? Sure. But they accepted those risks when they voluntarily got into the sub.