>>50216398
The fact they aren't physically youkai yet, or will ever become them is secondary to the fact humans being allowed to act like youkai undermines the de-facto caste system Gensokyo operates by.

If you want to know who enforces the law in Gensokyo when Reimu isn't breathing down them, the answer is Yukari and associates; a workforce of Zashiki-warashi tends to the villages' needs and provides them with a sense of luxury beyond what their station would give in the outside world, and also acts as a monitor to prevent the exact situation you're describing from festering.
There doesn't need to be a large force of village guards because the second one of these cutes spots something that would displease the sages, the information pipeline will quickly reach the Yakumo crew and Ran is noted to be a regular visitor of the village and can swiftly deal with anything that falls beyond the incident solvers' purview on her own, or more likely with Chen in animal form so nobody looks too deeply into her village persona (don't you know spotting a black cat is bad luck?)

Remember, the village is more or less 'in' on how Gensokyo works; the moment they deviate from the script too hard all the luxuries provided to them becomes their noose.