Official Notification
The point of a badge is official notification and recognition.
"Official" implies a framework of office. It further implies that there is an understanding or agreement in place regarding what that office is, and what its attendant duties, responsibilities, and privileges are.
There is no "office" associated with a "badge" that identifies an arbitrary function that has no attendant duties, responsibilities, or privileges.
To present a "badge" provides a visual cue that implies such an office and, there being no such office, amounts to pretense.
In the eye of the "badge" holder, there may be no intent to pretend to an office (though such an argument would be interesting to see played out), nonetheless in the eye of the beholder, the "badge" would carry false meaning (inference, if you prefer), and once the actuality of the "badge" was understood, a certain amount of emotional backlash might be expected. The beholder/observer would predictably feel fooled by the perceived pretense.
If the "beholder" happens to be an officially recognized office-holder (or "officer" if you prefer) whose office -- by publicly recognized convention -- is accompanied by an official badge of office, used for purposes of identification and recognition in the execution of the attendant duties and responsibilities and exercise of official privilege, and said officer concludes that the unofficial "badge" creates confusion about said duties and so on, a similar emotional backlash might well ensue.
An emotional backlash from bystanders and badged officials falls under the heading of something called "trouble."
The official unit of measure for "trouble" is the standard "heap."
And, while no actual laws may have been violated, one may, nonetheless, find oneself in a heap of trouble, or possibly several heaps.
Common parlance for decisions leading to heaps of trouble (or even a single heap) is usually expressed as "bad idea."
I'm sure there's a shorter way to explain this, but it seems to me the short explanation has been tried, and found insufficient traction.