This isn't really a problem. Ideas that originate outside the identitarian group still receive exposure and discussion within the group, and will be adopted and expanded upon if they are good ideas.

No, its the internet. We aren't dealing with rational human beings. We're dealing with internet users.

What will happen is that ideas will originate outside of the group. If these ideas already agree 100% with the predetermined values of the group, they will then acknowledge the ideas as legitimate. If the ideas do not 100% match, then people in the group will cry how its unfair and oppressive and destroying the community. They will complain until either the group in general comes to the consensus that they are correct or they go off and form their own splinter group based solely on the fact that they disagree with another group that is similar in almost every respect except against one issue.

In real life groups of people usually end up with at least some rational discussion, but social mechanics on the internet do not function in that manner. The vast majority of people only talk to the people in their group because they know that their opinions will not be challenged, and so when their opinions are challenged they react violently and personally offended. By and large people on the internet lose about half of their intelligence and replace it with a seething rage.