IMO the AS taking the Oaths contributes to the view society has on them. Why bind yourself if you can be trusted? The decision itself gives people the thought. It also gives AS the faulty belief that people think them "safe" ... Thereby allowing As to behave badly under the "protection" of the 3 Oaths.

If the AS never took the Oaths to start their actions would be the only thing people would have to go on, no comments about being careful to analyze the words of an AS etc. This alone would curb the number of DFs in the organization. If actions spoke louder than "words that cannot be untrue" DF would be hard pressed to stay hidden. As it is now all an AS has ever had to say is "I am not a DF" and she is immediately believed (well for 3000 years that was the case). Without Oaths someone might have looked a little more closely at what Marean was up too or ask a few more questions about Alvianrin's actions. Instead other AS literally took them at their word.