Statist claim: Only government can decide on punishment.
Fallacy:
"How are we [society?] to decide what punishments are suitable [for crimes]?" (Danny Smith)
Response:
Nobody has the innate authority to "punish" (punishment is arbitrary harm for arbitrary acts, including peaceful ones). Justice belongs to the victim, not "society" or any third party, who have no right to interfere except as agents acting on behalf of victim or criminal.
Also see:
Justice for more details on rational determination of just response to harm.
Rectification of Injustice, Chapter 10 of The Market for Liberty by Morris & Linda Tannehill.