The numbers must say otherwise. Has anyone actually seen the figures and formula used to do the staffing calculation?
I can suggest a number of ways to say 'no thanks'. Firstly just say 'no'. If you are busy - you are busy and that's it. Let the greedy ones take the money. When they get sick of it - let it go TIBA. That's why there are contingency plans. Who cares if you are the last one left to come in. I wouldn't think coercion would be endorsed. You are entitled to have a life - that is why you go to work.
If the figures say the staffing is OK and the airspace never closes it is easy to justify that everything is OK - maybe it is. There is not much EVIDENCE to say otherwise. Blame the complaining on the complaining ATC's - industry will believe it - next thing they will want a huge payrise.
The Department of Transport and major airlines would not tolerate systematic airspace closures.
If the system is as broken as people are indicating then let it show - stop holding it together at the expense of your life. Sometimes complete inaction is all it takes.
If you try inaction and everything still rolls on - good, it mustn't be that bad after all and at least you will enjoy your life.