The root cause of violent extremism is not that an ideology exists. The question to ask is *why* someone would find that ideology convincing. The reasons for that are virtually always personal, not ideological. Pressured communities are full of potential customers.

Also, even in the lack of an ideology, potential customers can simply concoct their own ideology that answers their needs, of simply concoct an elaborate conspiracy theory that skips ideology altogether. Look at QAnon for example.

The "breeding grounds" of violent extremism are not ideologies - they're disenfranchisement, alienation, crises of identity & purpose, anger, feeling like you don't belong and don't matter, etc. Once someone feels like that, they'll seek out an ideology that suits them.

The ideology is an answer. Find the question.
The ideology is a product. Find why they want to buy it.