Nasty people do exist in any environment, but in just the same way that network effects can enormously magnify things like charitable fundraising or the production of cat memes, they can also amplify the production of terrorism or other undesirable activities. Damaging social infrastructure which allows that is an effective way to impede recruitment and organization.
Ban free association then if you are worried about the wrong ideas being propogated to people. Build the police state and massive bureacracy that can enforce this at that the detriment to us all, or start trying to engage with these people and solve the fundamental problem.
Nasty people do exist in any environment, but in just the same way that network effects can enormously magnify things like charitable fundraising or the production of cat memes, they can also amplify the production of terrorism or other undesirable activities. Damaging social infrastructure which allows that is an effective way to impede recruitment and organization.