For one, it is necessary to detail how you arrived at that conclusion to convince others as well. Even though it could be counter productive by making scammers more aware, it is a necessary system.
What I am proposing would only make sense if scammers and wrongdoers were banned by the forum admins. Since that is not case, it doesn't really matter.
Let's say you caught someone in the act of scamming. You have the needed proof to have him banned, but instead of revealing everything in public, all you need to do is present the evidence to those who make the decisions about who gets banned. That's theymos and Cyrus, and possibly other members of the staff who are included in that decision-making process.
Why only them and not the whole Bitcointalk community?
The Bitcointalk community doesn't have a say in who gets banned anyway. theymos doesn't ask the community if he should ban user X or not. He either bans someone or he doesn't. User X will be told he got banned and the reason why. If he wants more information or proof, he can take it up with the forum admins who again make the final decisions whether user X will be unbanned or not.
The usual Meta threads can still be started to appeal the ban or offer support to have user X reinstated.
But since scammers are not a priority, none of this will ever happen.