Why capture the spacecraft?

Why did they bother to capture the American and Soviet space capsules? They have the capability to intercept the spacecraft, so instead of sending a fancy manned craft, why not just a simple missile with a warhead? Boom, and that's war. The missiles wouldn't have to return to base, so that would eliminate the danger of being tracked back during the landing. They never said they needed the astronauts and cosmonauts alive for any reason. For that matter, they didn't need the captured spacecraft, either, and even Blofeld admitted that by ordering the destruction of the third one as soon as it's captured.

Then again, they did much the same thing in the Roger Moore remake, The Spy Who Loved Me. The nuclear subs were all they needed, but they took the crews as live prisoners just so there would be people to fight back in the big climax.