The police are remarkably good at what they do, and that includes police officers acting in an undercover capacity. Sometimes there might be obstacles that they will have to carefully consider. The question really is, if there are obstacles they have to carefully consider, does that justify the alternative?
You give the example of the small town. Does that justify the alternative of the police enlisting the services of the thug, the thief, the drug addict, the drug trafficker from the small town, and asking that individual to commit an assault on behalf of the police because the police are not able to do it, but that's what they believe their investigation warrants? In plain language, that can't be right