The statement in question commits the slippery slope fallacy because it assumes that legalizing psychedelic mushrooms for medical use will inevitably lead to widespread recreational use and negative consequences, without sufficient evidence.
The statement "If we legalize psychedelic mushrooms for medical use like Oregon has, soon everyone will start using them and then use opioids, leading to crime and overcrowded jails!" commits the slippery slope fallacy.
This is a type of fallacious reasoning where the argument proposes that a relatively small first step leads inevitably to a chain of related events culminating in some significant impact, without providing sufficient evidence to support the inevitable chain of events.
The claim suggests that if psychedelic mushrooms are legalized for medical purposes, it will automatically result in widespread recreational use and a cascade of negative outcomes like opioid use, crime, and overcrowded jails, which is a large assumption with little evidence provided to back it up.