Any Islamist group that is not created for, and dedicated to a specific purpose, should only envision itself as an umbrella organization to promote the general Islamic project. What do I mean by that?
A group should be formed for a particular task, a particular and specific mission with a clearly defined mandate. For instance, feeding the poor, or teaching people how to read and write, or for targeting foreign investment for disruption, etc. Its purpose must be specific and its effectiveness quantifiable.
A group should not envision itself as the embodiment and representatives of the religion of Islam itself. If the group wants to serve a general purpose, then it must necessarily be flexible and inclusive, and give its support to other groups engaged in Islamic work, even if the other group does not adhere to their own particular school of thought. If they do not do this, I am afraid they will fall into the common error of regarding their group as the owners of Truth, as the “Saved Sect” referred to in the hadiths, and they will ultimately begin to function like a cult. It will not be long before they move from the point of thinking all non-group members are wrong to thinking that all non-group members are not even really Muslims.