It isn't the vacuum that causes the capsule to collapse but the atmospheric pressure outside of the capsule that causes it to collapse. It is exactly the same with a submarine. It is impossible for humans to survive pressurizing the inside of a submarine to equal the thousands of pounds per square inch water pressure on the outside of the submarine. The submarine implodes if a breach in the vessel occurs. A breach in a spacecraft or an aircraft at 30,000 feet causes the spacecraft or aircraft to explode into the lower pressure outside. Space is a vacuum because it has a volume without molecular pressure that is so vast it approaches infinite. There are vast interstellar clouds of molecules in space but they are so widely dispersed that the pressure is still so miniscule as to be a vacuum by comparison to the atmospheric pressure at 150,000 feet above the Earth's surface.