Do not say about any group “they are good” or “they are bad”; or “they are right” or “they are wrong”. Every group is all of these things. And know that any group may be extremist in some matters and not so in others; and to make a blanket statement about them without making these distinctions, is itself a kind of extreme position.
Every group makes mistakes in their ideology, their actions, and their strategies; this does not make them entirely corrupt or deviant.
I have written several times about what I believe are the mistakes of, for example, Da’esh or the Ikhwan, but I also recognize and acknowledge the things I believe are good about them.
Try to maintain your objectivity, even if you join a group; especially if you join a group, actually, although it will be much more difficult for you to do so once you immerse yourself in the group structure and surround yourself with its members. If you truly believe in the goals of the group, and believe that it has the capability to potentially achieve those goals, the best contribution you can make to that effort is to exercise objective criticism. And if the group does not tolerate this, than know it is pregnant with its own defeat.