One easily falls to the trap of thinking that disagreements with other people happen because the others are irrational in simple, obviously flawed ways. It's harder to avoid the fundamental attribution error and the typical mind fallacy, and admit that the others may have a non-insane reason for their disagreement.

Harder, not harder, but which is actually right? This is not about signaling one's ability to do the harder thing.

The reasons you listed are not ones moving most people to not sign up for cryonics. Most people, as you mention at the beginning, simply don't take the possibility seriously enough to even consider it in detail.