A community is an association of persons united by a common good. The nature of that good determines the nature of the association which is ordered to it.
If an association does not have a good as its unitive principle, then it is not, properly speaking, a community. However, as persons associate for a variety of specific intentions, and it is impossible to intend an evil per se, there is no association that is evil per se. However, while there can always be found at least a vestigial good by which every personal association is sought, an association that is not oriented to a common good only has the appearance of a community.
An association that is made purely from individual intentions, and thus fails to give rise to communion, might be called an "evil society" if it is directly detrimental to the attainment of any common good. As a corpse or a wax sculpture might resemble a living creature, so can an evil society resemble a community.
The most prevalent kind of evil society is a kind of economic association; that is, an association that is sought for purely economic intentions; that is, aimed at the acquisition of individual -- i.e. material -- goods. Both crime syndicates and large-scale corporations can have such a character.
There can be real communities of a purely economic nature, so long as they serve a common good by providing for the material resources necessary for its fulfilment. But, of course, without a proper relation to the common good, such associations are not communities properly speaking. Furthermore, it is likely that such an association (whose intended goods, though individual, are necessary for the attainment of higher goods) is a serious detriment to the development of real community. In other words, it is quite rare to find an innocuous economic association which is not immediately subordinated to the common good.
He who has authority over a community will therefore find such evil societies to be his greatest enemies.
