There's a much better, simpler reason to reject cryonics: it isn't proven. There might be some good signs and indications, but it's still rather murky in there.

This is a very bad argument. First, all claims are probabilistic, so it isn't even clear what you mean by proof. Second of all, I could under the exact same logic say that one shouldn't try anything that involves technology that doesn't exist yet because we don't know if it will actually work. So the argument has to fail.