SC
I am glad to see you are coming back to the central issue. I agree that any extra task can be the thin end of the wedge, and it is the duty of any responsible union to keep an eye on this.
And yes - the tricky bit is where to draw the line. It's basically a judgement call, and I suggest a large helping of common sense is the most helpful tool in this, together with a good look at the wider issues.
If you are just playing devil's advocate, fair enough. But if you are really agonising over this decision, a quick re-read of the hundreds (thousands?) of posts on these forums may be of assistance. Also, BASSA's insistence on a H&S committee review of the dangeous task of lowering a blind may give you a clue about who is acting in good faith here.