Thing is, we cruise with P&O as they offer excellent value when you include everything (i.e. tips, total bar bill etc). If they decide to maximise their profits (as is every company's duty to its shareholders) and this means that they are no longer considerably more attractive, total price wise, then I will go to another cruise line - there are an awful lot to choose from. If enough people follow me then P&O will have to look at a different model for maximising profit.
The current changes, to me, are not too unreasonable and won't yet make me change my preference. If they continue down this line then, obviously, the calculation changes.