There's a much better, simpler reason to reject cryonics: it isn't proven.

That's a widely acknowledged fact. And, if you make that your actual reason for rejecting cryonics, there are some implications that follow from that: for instance, that we should be investing massively more in research aiming to provide proof than we currently are.

The arguments we tend to hear are more along the lines of "it's not proven, it's an expensive eccentricity, it's morally wrong, and besides even if it were proved to work I don't believe I'd wake up as me so I wouldn't want it".