It teaches them to be critical thinkers instead of community sheep later in life and are prepared when the real scammers show up.
Although I hate arguments being compared to real life, I slightly agree with it. However, it doesn't explain why they shouldn't get a negative for promoting/supporting the ponzi, which will lead to more users being scammed
It is really not that hard to explain. A red trust is a warning. Warnings make you aware something is up. They work because they aren't always around us. But when every participant has the same warning on their profile it loses it's message.
When a noob googles bitcoindoubler and comes to the subforum and sees everyone with with negative trust it is nothing special anymore and I doubt they will check it.
A negative trust, a warning should not be giving lightly in my opinion for that exact reason. It should stand out when visiting a page. And it will lose its message in that subforum when everyone wears that tag.