> domain.net part is still susceptible to being seized

Yes it is, but how do you discover the domains? There could be just a few hundred users per domain. Then you have to expend substantial effort to seize each domain.

Meanwhile any affected user just moves to their second domain. Even if the authorities got much better at taking down domains the only issue would be increasing the number of extra domains per user.

I can't see how the authorities can beat this.