Ah, OK. No, the idea is that groups of like-minded people are more likely to change their beliefs than are more diverse groups. This is, among other things, an explanation for how groups of individuals with extremist tendencies turn into extremist groups.

In addition, the more extreme their starting beliefs are, the more dramatic the even-more-extremifying shift is. If I put a bunch of Democrats in a room for a while, they will come out as somewhat more liberal Democrats, but if I put a bunch of socialists in a room for a while, they'll emerge as revolutionary Communists.