The 'censorship road' is one I highly doubt the admins would want to take, even for proven scams. Scams are everywhere on the internet and is a big issue for forums, but limiting certain proven scammers and locking their threads would likely do more harm than good;
If that is the only way to eradicate scams and make them not come back from the dead then I think that it is worth the shot to try it out as an experiment first, just because you are censoring does not mean that you are restricting a free speech, everyone has a right to their opinion yes but others have the right to not hear it if they deem it unfit in ethical standard.
• The admins and moderators would be policing scams and would have to employ lots of resources to try and prove these scams which is not always possible to do,
Scambusters are there to do the job, they just need to be sure that it is a proven scammer before presenting it to a higher level.
• It would give users the impression that the forum checks scams and as such it's safe to interact with users who have not been caught, this could cause them to let down their guard,
Locking the topic doesn't mean that people will not be aware, reports of other scams are happening in the board so the newbies that will check it won't miss out so much as most scams are almost the same.
• It could lead to lots of posts complaining about selective censoring,
The only ones that will be censored are the ones that are proven scammers so it does not matter that they are complaining.
• Bitcoin is considered a free network, and the forum is expected to reflect that quality as well.
Free does not mean that you are also free to do harm when it is blatantly obvious you are doing so, if it is free then that means that shutting them down is a free thing to do too.
The current system seems to be the most ideal and has been effective in warning members who actually pay attention.
It does work in a certain degree but if we were to put an iron grip on regulating and eradicating this scams will be more effective.