I don’t think I made that argument, in fact, my comment was made specifically without the qualifier of it being legal vs. illegal. Manipulation (which let’s face it, social engineering is a fancy way of saying) is a pretty solid example of an unethical behavior depending on your ethical world view. Utilitarian? Great, you must also think torture is acceptable so long as it saves lives. Deontological ethical world views might have something different to say, speaking of Germans (e.g., Kant).

Regardless, I think contriving scenarios where you think someone may act corruptly just to catch them doing so is equally as unethical as a police officer encouraging someone to commit a terrorist act then arresting them once they do.

It is manipulative, may not have happened otherwise if not for the original actor, and is akin to saying “I hope you don’t behave like I’d expect a human to instinctually behave if put in a corner”.