From earlier in this blog: "A lie is justified if it does not benefit you." Of course, most of the time the lies that people tell end up benefiting them because of the actions or prejudices of other people, even if the lie could not reasonably be expected to be believed. Due to the indirect influence of people and situations that surround those that encounter these lies, it becomes more efficient both on an individual level and on the level of the society to believe them. This, of course, is why crime exists, since it will always compete with the administrative and social effort needed to control it.
In some cases, however, whether something is a lie at all depends on other people, and this may mean it is the responsibility of someone else to ensure the above situation with regards to purity, even when the implications of this are an unwanted result.