I was a student at Manchester University years ago and this crap was going around then. The bean munching, wooly jumper wearing pacifist twats would occasionally picket outside the OTC building, or hold peace rallies and decry the armed forces.
The point is that the Student Union is a complete irrelevance to most people. The only connection anyone I knew at Uni had to the Union was to drink in the Serpent bar as it was then because it was cheap. Most students will crack on with their own lives and make choices based on balanced information, not the one sided drivel spouted by the Student Union.
If they ban the military from campus the next step will be to the ban the investment banks (now there's an evil empire!!) from the milkrounds as they represent all that is bad about capitalism.