(Okay, one final comment about this subject and then I'll stand down here, I promise.)

In order to render the cabin's internal climate acceptable at a cruising altitude of 30-36,000 feet, the air inside the aircraft cabin is kept at the equivalent of 8,000 feet. As the plane gains altitude, the difference in pressure between the air in the cabin and the air outside increases. Pressurization exerts physical forces on any potential weak point in the aircraft structure, and that includes its doors and cargo hold latches.

For example, if the seal on a cargo door fails, as occurred on United Airlines Flt. 811 only 20 minutes after it departed Honolulu for Auckland in Feb. 1989, it can result in a massive explosive decompression, which in this tragic instance swept nine business-class passengers through the resultant fuselage breach to their deaths.

(It's worth reading the Wikipedia account of UA811's ordeal, if only to understand the seriousness of explosive decompression in an aircraft at high altitude, and the very fine line the flight crew walked in their heroic efforts to nurse that B-747 back to Honolulu before all its systems failed completely.)

Survivors from UA811 all testified at the NTSB hearings that they heard an explosion, which the flight deck crew initially and mistakenly attributed to a bomb in the cargo hold. Federal investigators later surmised that had the airliner been at its initial assigned cruising altitude of 35,000 feet, rather than still climbing at 22,000 feet, when that cargo door's seal failed, it's quite likely that the entire aircraft would have broken up mid-flight and its entire complement of 355 passengers and crewmembers would have been lost. As it was, UA811 barely made it back to HNL on its two surviving starboard engines.

That's why the proficiency of an airline's ground, cabin and flight deck crews really matters, as they each go through their respective pre-flight check lists. The failure to ensure that a cabin door or cargo door is sufficiently closed and sealed can otherwise lead to catastrophe once a plane climbs above 20,000 feet.

But in UA811's case, no such attention to detail by the crew could have prevented what occurred on that 18-year-old B-747. Investigators determined that a short circuit within that aircraft's aging electrical system caused an unprompted rotation of the cargo door's latches, effectively compromising its proper seal and consigning UA811 to its fate.

In that regard, it's perhaps worth remembering that the Metrojet A-321 aircraft in question was also 18 years old at the time of its crash. And that's why it's so vitally important here to let investigators on the ground in Sinai do their jobs, and not speculate publicly about bombs and terrorism in the present absence of any conclusive findings to that effect.

The flight cancellations are not because the airspace is dangerous, it's because they don't trust the security at the airport.  Brittan has sent people there to help scanners, scan baggage, but I am guessing it's more to make sure ISIS doesn't have a plant on the inside.
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Acting TSA Director Reassigned After Screeners Failed Tests to Detect Explosives, Weapons(June 2, 2015)

Washington (CNN)The Department of Homeland Security said Monday that the acting administrator for the Transportation Security Administration would be reassigned, following a report that airport screeners failed to detect explosives and weapons in nearly every test that an undercover team conducted at dozens of airports.

According to a report based on an internal investigation, "red teams" with the Department of Homeland Security's Office of the Inspector General were able to get banned items through the screening process in 67 out of 70 tests it conducted across the nation.