Imagine a volcano is about to destroy an island and we go to local villages telling the natives boats are waiting at the shore, and urging people to leave without delay. It would be odd to object saying their lives somewhere else will be different enough to make them different people, and so the world would be better off just raising new people to live in those other places. Perhaps you just want us to remind people that maybe they would really rather just die than live such a different life, but even that seems a bit odd.
You could make a similar argument against the retirement of folks whose identity is tied up closely in their jobs; they should either keep working till they drop or commit suicide the moment they stop working. After all, they aren't nearly as useful to the world in retirement as in work. You might say it is their continued connections to family and friends that justifies their staying alive in retirement, but we also urge people to be frozen together with their family and friends.
It is too easy to slip into the mode of assuming that each thing we do that effects the future must be in their interest; we can instead trade with the future. In a voluntary trade, each side expects to benefit from the whole package, but not usually from each part of the trade. Ordinary interest rates make it very cheap for us to benefit the distant future by enormous amounts just via savings, making enormous gains from trade possible if only there were things we wanted from the future. Cryonics revival is such a thing we can want from them.
It really is a terrible shame people feel so free to ignore the wishes of ancestors who sacrificed to benefit them. The law often allows us to violate the letter and intent of wills when that seems in our interest. We should instead be trying to promote more trade across the generations, by trying to give our ancestors whatever they wanted and reasonably paid for. We should promote such a norm of not breaking deals not just out of fairness, but also so that our descendants will not break our deals with them.
If I want to live longer in the distant future, even as a "different" person, and am willing to save a bit more now to pay for it, why isn't it enough that this is a win-win package deal?