To call it having something you thought you'd be given delayed is rather to understate the issue.
People have been given to understand that they would get the pension at 60. Now they won't. 3.8m women are affected. How much they lose depends on things like when they were born, but some lose up to £50k. For some, there may be an option of continuing in employment. For many, there won't. The outcome for many will be hardship and poverty, for a situation not of their making.
The justification is that differential pension ages is discriminatory. The decision to deal with that by penalising millions of people who did not create the discrimination is morally unacceptable.
People rely on this pension. It's not like a prospective bonus which they now won't get, it's the core income on which most of them will depend.
On top of that, they have been told for many years that we pay into the system via NI, and we get back the advertised benefits. The fact that the internal workings of government finances don't quite work that way isn't the point - there is an expectation that has been created, and the breach of this expectation is a breach of a type of contract between rulers and ruled. It is a betrayal of the worst kind.