The reason the student needs the source is that 'quals' are used to quickly legitimize a person's argument. In policy debate, unrefuted arguments are considered true. Thus, there's little time for intelligently evaluating what a person is saying, as long as they have 'quals' and you can get to the next piece of evidence ('cards'). The most outrageous argument from a PhD might be preferred in debate over a rational argument from an intelligent person, like Charlie Stross. edit: That's why he can't just say 'as Stross says...' like the commenters suggest. As an example, this past year my debate topic was mental health. I often cited Robert Whitaker, who is a finalist for the Pulitzer prize for psychiatric journalism, was the former director of publications at HMS, and has written two books on psychiatric medications. Yet, because he did not have an MD or PhD, debaters sneered at his qualifications, rather than evaluate his arguments.
I also find it highly likely that Stross's article is being used because of this paragraph "Historically, crossing oceans and setting up farmsteads on new lands conveniently stripped of indigenous inhabitants by disease has been a cost-effective proposition. But the scale factor involved in space travel is strongly counter-intuitive."
This is because debaters often don't respond to the other's policy proposition, but rather kritik their position by indicting the philosophical ideas behind it. For example, an affirmative debater might advocate colonizing a planet, and a negative debater could ignore this and talk about how the affirmative is really based on white-power dominance of other cultures, and thus they should lose.
My quals: debater in a different type of debate