Surely the issue with only using your own knowledge is that it will produce conclusions that are in line with your method of thinking and assembling facts - which undermines the objectivity requirement. Trivially, I know that some of the things I believe to be true are in fact false, so consulting other sources can help identify these incorrect statements when coming to a conclusion.

As an example, look at the worked example: I understand the final statement to be incorrect - the claim that having more charlatans about making each of them individually weaker doesn't fit with the 'survival of the fittest' model. Rather, if the resource (people to be scammed) is finite^ then competition will result in the most able charlatans being able to stay in the market whilst the less able are driven out of it. The point to take away from this is that if you increase the supply of potential charlatans but keep the limit on the number of charlatans fixed then those that 'survive' will be a better fit for their environment - i.e. better at scamming.

Looking at the conclusion you appeared to come to, the consensus"" that I am aware of is that some information should be controlled - knowledge of how to manufacture explosives, for example, is generally prohibited knowledge for individuals (needless to say, the advent of the internet made that a touch more challenging) whilst the knowledge of how to produce, support and deploy nuclear weapons is very carefully guarded by the governments possessing it. As such, I do not believe that your conclusion that knowledge being freely available being a net positive is true in all cases. 

I don't deny that a lot of conclusions and decisions are made quickly and based solely on one's own knowledge, and usually that isn't an issue (in the grand scheme of things, choosing what to have for dinner is a fairly inconsequential decision*) but conclusions and decision-making of any significance should always be subjected to input from other viewpoints, and ideally should be formulated into a testable hypothesis. Being able to consider the information available is a useful skill, but as you are always working with an imperfect data set you should be exceptionally careful about claiming objectivity (indeed, exactly what constitutes 'objectivity' is itself slightly tricky as there are different definitions that are not always made clear when the word is used.) 

^which is true, but assuming that the existing charlatans are fully exploiting it is not true

""I defer to consensus as I only have limited knowledge of information management, and so assume that the consensus has been considered and tested and so is correct in this instance - there is a place (indeed, there is a need) for radical thought to challenge the consensus view, but not from me in this specific instance as I lack the knowledge to do so

*although setting a policy on what you should generally be having for dinner is perhaps worthy of more thought.