You have to ask yourself why?
I suppose there isn't really any need for you to understand why. The city understands perfectly, and judging by the share price rises they are expecting exactly the same win at Iberia. I read somewhere that IAG have €550m set aside for the battle. The Iberia unions can choose to cut off their noses to spite their faces if they so decide, but whether they are justified in their fight or not, they are not going to win against that kind of determination. BA's cabin crew had no chance of winning either. It doesn't matter what anyone thought about whether the attack was justified, fair or necessary. All that matters is the company wide cost savings were demanded and then they were achieved. Unfortunately for the effected Iberia employees, the same will happen in Spain.
By extension, any work group (including the BA pilots) that attempts to hang on to wildly above market rate terms and conditions going forwards, will have similar demands made of them, and with equal determination. In a company with lots of people doing the exact same job, such as within an airline, unions are necessary for collective negotiation and bargaining. However, gone are the days of unions holding companies to ransom.