Exactly this is the problem. There is nothing fundamentally wrong with frontier justice, the only problem is that people don't act rationally in general. What if it is not some lost money but if someone got badly hurt, raped or killed? Can you hold back your emotions? Make sure that you are not targeting the wrong person? And even in the case of this story, what if those two guys are themselves just victims of the real scammer hiding behind their identities? You just publicly stigmatized two innocent people as scammers.