If PKU students are allowed to organize a march inside the campus, what would they march for/against? Democracy? Anti-Japan? The so-called normal-distribution grading system? The poor services provided by many university staffs? The current campus traffic planning? All seem plausible.
So what if PKU students march for all of these troublesome issues at the same time? One gets a march for democracy, because democracy is nothing, but anything, solves no problem, but every problem. That's pretty much how I perceive the HK march.
Anyway, a clever central government would give more democracy to HK, I think.