People who want to destroy democracy are influenced by their brain too. But they do react more extremely than others.

The thesis here is consistent with people believing political violence is justified, with human brain's tendency to form a "us vs them" mentality. But it doesn't explain why some act more extreme and violently.

People react differently because of multiple factors, such as living through different circumstances, different cultures, being more or less subject to cognitive biases, seing more or less misinformation, ... For instance if you see more misinformation about polical adversary being evil, AND your biases and culture makes you more likely to believe it.

That isn't an excuse for any violence. Understanding these mechanisms may help prevent reduce violence or hate. That's a worthy goal even if some groups have a much greater responsibility for political violence.