Whether one agrees with the goal in the abstract may be different from whether one agrees with the goal as expressed or as likely to be executed by a government or party.
I don’t think anyone is saying repression is the sole cause of fundamentalism, there is a lot of prior history, only that it’s a major factor in it’s spread. In an extreame environment the moderates become invisible and largely ineffective, at least in the short term. Fundamentalists can exploit and channel the people’s anger to gain recruits. I’d agree we shouldn’t take the “expression of rage” theory as gospel.
Did the supression increase or decrease the brotherhood’s membership? Or more to the point, did the supression make it easier for it’s militant wing to justify it’s actions and gain support?
Or have the fundamentalist Islamic countrys just been more successful at supressing their populations, by aligning themselves with religious authority?