From a sociologist's point of view, can it be argued that groups need deviant people?
Yes, it is most definitely possible to argue from a sociological point of view that deviance is important for a group. The argument is that deviants make it much easier for a group to maintain its identity and its cohesion.
In order for a group to remain together, its members have to feel in some way connected to one another. This can be very difficult, particularly if a group is very large. The interpersonal ties that bind the various individuals can be rather weak when the group is large. This is where deviants come in.
Deviants help a group to define itself. The way they do this is by showing what people in that group do not do. In other words, they are a negative example. By acting in ways that are wrong, they remind the people in the group which actions are right. They also allow the group to have an “other” of sorts. The people in the group can define themselves as people who are not like the deviants.
Thus, the presence of deviants makes it easier for a group to remain connected and cohesive.