The argument is that scams based on exploiting goodness causes a lot more harm compared to the ones based on exploiting greed. Because it trains people that doing good deeds is not worth it (they might be scammed.) And even if the rate of such scams are low, just reading about them makes people afraid of potential consequences of doing good deeds. So I absolutely agree that such scams should have very harsh punishments, because they do not only have immediate consequences, but they degrade trust in our society.