But surely fewer channels means fewer recruits? Ultimately it's about what kind of content these platforms want to publish though.

It might also mean "higher quality recruits".

And that’s okay. Fewer “higher quality” recruits are easier to go after individually.

History says that well-organized, even if smaller movements, have higher chances of achieving their goals.

I can recommend this article about inefficiency of online movements:

https://www.theatlantic.com/technology/archive/2019/05/in-pe...

You can say the same about forces that work against the criminals as well except they’re well organized and have larger numbers.

Your link doesn’t take into account if the chilling effect is what leads to ephemeral online hate movements.

The more someone has to rely on backup channels and then backups of the back channel, the less likely you enroll new members.

As I said elsewhere in this thread (and linked to an article on similar topic), success isn't measured by sheer numbers of lukewarm sympathisers alone.

It is not as if George Washington or the Civil Rights Movement recruited masses of followers online. They started with relatively small but cohesive units. Yes, it took them longer than it takes today to assemble a flash mob. But the efficiency measured by capability was higher than today.

For an example, if I were a German cop, I would be much more concerned about the mostly-offline groups such as the Reichsburger or the Grey Wolves (Turkish nationalists). They linger around for decades and are hard to penetrate, unlike whatever wild crowd you can put together on Facebook. That Facebook group will look scary, but it won't have much pull after 5 years, because it competes with a ton of other Facebook groups for attention.

Even so, it makes very little sense to provide a platform to these hardcore organizations to continue to recruit from. The dismantling of the old KKK in the United States is a great success story to work off of.

Person to person doesn't scale as well as the internet.

Again: yes, it does not scale as well. But scale to what? Silicon Valley is generally obsessed with quick growth without thinking about long term impact. But politics is generally long term.

It is easy to put together a temporary, unstable mob of people in virtual reality. But real political impact of such mobs tends to be superficial.

Impactful organizations such as, well, the Taliban, sacrifice rapid growth and substitute it with higher-quality personal connections.