I'm afraid there are quite a few grievous errors in the article... surprising from National Geographic, but for posteriority, we'd like to clarify some things. All quotes are taken directly from the article.
"They say the species is the biggest and most fearsome squid known to science and could grow to 40 feet (12 meters) in length—longer than a whale."
Longer than a juvenile sperm whale. Adult sperm whales reach 18m, half again as long as either Mesonychoteuthis or Architeuthis (max ~13m).
"Jules Verne's Twenty Thousand Leagues Under the Sea, which later became a Disney movie, featured an encounter between a colossal squid and a French naval vessel."
It was a giant squid, Architeuthis dux.
"Thought to be only the second intact example ever recovered, the massive cephalopod was armed with four huge beaks and rotating hooks along its tentacles and arms."
The second reported intact specimen.
ALL squid have TWO BEAKS, one upper and one lower.
The hooks on the tentacle clubs swivel; those on the arms do not.
"New Zealand squid expert Steve O'Shea, from Auckland University of Technology, has described the squid as 'a true monster.' He told the BBC: 'Giant squid is no longer the largest squid that's out there. We've got something that's even larger, and not just larger but an order of magnitude meaner.'
"Auckland University of Technology research associate Kat Bolstad, also talking to the BBC, added: 'This animal, armed as it is with the hooks and the beak that it has, not only is colossal in size but is going to be a phenomenal predator and something you are not going to want to meet in the water.'
"Other scientists dismiss such claims."
What claims? Mesonychoteuthis is, if not longer, more massive than Architeuthis at similar lengths.
Obviously humans are not a part of the colossal squid's diet. They wouldn't be a natural part of a Tyrannosaurus rex's diet either. That doesn't mean such an animal wouldn't kill and eat one given the chance. It might not - but I'd rather not find out.
"Richard Ellis... 'wrote The Search for the Giant Squid to try and dispel some of the crazy ideas that this cephalopod is in any way dangerous to humans, and the same holds true for Mesonychoteuthis.' "
This implies that we are perpetuating myths.
No deep-sea cephalopod can possibly be a direct danger to humans, in the sense of the public at large, because there is no way for accidental encounters to occur. People do not live in the deep sea. Cephalopods do not live on land. There is no common ground.
Since adult Architeuthis do not occur in surface waters, they cannot even be encountered by divers. Mesonychoteuthis is recorded solely from Antarctica, so the possibility of encounters is remote, as diving in the Antarctic is an infrequent occurrence. It would technically be possible for a diver there to encounter a colossal squid, as they do occasionally range to the surface. In the highly unlikely event that such encounter took place, I certainly wouldn't want to be the diver. In that sense, in the fantastically remote possibility that a diver, or fisherman accidentally, were in the water, I think is is safe to say that Mesonychoteuthis could be dangerous.
"Some of the earliest tales about huge, tentacled sea monsters date back to the 12th century when Norwegian seafarers described an awesome beast called a Kraken.
By the 18th century the Kraken still had a fearsome reputation. In The Natural History of Norway, the Bishop of Bergen likened it to a "floating island," adding, "It seems these are the creature's arms, and, it is said, if they were to lay hold of the largest man-of-war [a ship], they would pull it down to the bottom."
More myths we always mention in the context of their improbability.
"There is also an account of sailors being attacked by a giant squid after their ship sunk during the Second World War. At least one sailor was supposedly eaten. And even this year, French yachtsmen taking part in the appropriately named Jules Verne Trophy reported that a 26-foot-long (8-meter) squid clamped itself to their boat."
A giant squid cannot consume a human, at least in any short period of time. It is a physical impossibility. The esophagus of Architeuthis is a maximum of 1 cm in diameter and passes through the brain. Obviously larger objects, or sharp ones, cannot be swallowed. Also, refer to the pictures of the Architeuthis beak - this animal can cut through flesh, certainly, but not mammalian bone. And again, the adult giant squid does not occur live at the surface.
The French yachstmen who reported the giant squid have since admitted that it was a hoax.