Your response is too fast, and so ill considered.

For example: The point about a Molniya orbit is not that it is stationary with any given piece of debris. It is relatively stationary with a fixed point (relative to the earth surface moving at what? 10.7 km/s) above the earth's surface for a protracted period of time. So if a piece of debris was moving in that frame of reference for a small part of that time, a collision could be arranged.

Now, if you put the deflector into a highy elliptical orbit specially chosen to (after the manner of the Molniya orbit) cause the deflector to be moving at a low relative velocity (relative to the piece of debris) for the short period of time of the collision, then all the problems associated with high absolute velocities disappear.

Update: You're right about the Molniya orbit. The apparent "apogee dwell" is due to 1) moving more slowly at the apogee. 2) the small arc of the sky covered (as seen from earth, during the long climb and descent to and from apogee. The relative speed to any given point in space is not vastly reduced. Just the apparent speed across the sky. That still leaves the question of how a paper aeroplane thrown from ISS makes it to earth in a few months with only the strngth of an astronaughts arm to change it velocity?

(I'd already read apl's post and dismissed is because his banks of earth aren't moving. I also mentioned the speck of paint and the shuttle window incident above. Were the two travelling at slow relative speeds? No. Likely as not they were travelling in opposite directions at the point of encounter!)

You've already agreed that if the two components are in the same orbit with one moving slightly slower than the other (the docking scenario), then their absolute velocities is irrelevant.

The point about the Molniya orbit is that it demonstrates that the two components, the satellite and the point above the earth can be travelling in entirely different orbits at vastly different speeds, but for some period (including fairly protracted ones), of their cycles, they are travelling co-incident to each and at low, relative speeds.

Your other points are just spoilers:

• Small particles:

  a) I said I think. Not a "claim".

  b) Not all the small particles from any given source of course. Especially not all the particles from an explosion or collision. But are you prepared to deny that any 2 or more small particles will follow similar orbits for a protrated period?

• Drag effects and size:

  Like I said, the math gets complicated. Have you considered the terminal velocity affect? The idea that a thing falling to earth under gravity will reach a maximum velocity and no more.

• How does your physics intuition rate the chances of a paper aeroplane being launched by hand from ISS reaching the earth's surface?

  Because at least one scientist believes that it will. Yup! A piece of paper with a launch speed relative to the ISS of whatever an astronaut can generate with his arm. Does that give you any pause for thought?

  Or is that scientist just crazy to think that such a small change in absolute velocity from the ISS' 27,700 kph could result in an orbit that would return that piece of paper to earth in a reasonable time frame ("several months" according to the scientist)?