Science fiction has a bias towards things going wrong.

In the particular case of cryonics, if there's a dystopian future where the majority of people have few or no rights, it's a disaster all around, but as ata says, you can presumably commit suicide. There's a chance that even that will be unfeasible-- for example if brains are used, while conscious, for their processing power. This doesn't seem likely, but I don't know how to evaluate it in detail.

The other case-- people in general have rights, but thawed people, or thawed people from before a certain point in time, do not-- requires that thawed people do not have a constituency. This doesn't seem terribly likely, though as I recall, Niven has it that it takes a very long time for thawing to be developed.

Normally, I would expect for there to be commercial and legal pressures for thawed people to be treated decently. (I've never seen an sf story in which thawed people are a political football, but it's an interesting premise.)

I think the trend is towards better futures (including richer, with less reason to enslave people), but there's no guarantee. I think it's much more likely that frozen people won't be revived than that they'll be revived into a bad situation.