Their argument is this:
" - We want to disrupt the university as much as possible,
- the university's main business is students,
- therefore the best way to disrupt the university is to disrupt the students.
- However, we're not seriously damaging the lives of students as they can apply to us for marks anyway."
The problem as I see it is that most students don't know that they can apply for their marks, and if you argue that students can get their marks, you can't argue that you're actually being disruptive. Ie you can't have your cake and eat it too.
People who work in the tertiary sector (teachers particularly) seem to have a very high standard of living within their workplace; their hours are far more flexible and forgiving than elsewhere in the world. Furthermore, much of what the union is complaining about would have been apparent to the teachers before applying for their jobs - that is to say they couldn't argue that they 'Didn't sign up for it.'