You can't know anything, but you can form beliefs that have various levels of confidence. For example, there is reporting about the objective reach of Jones' properties post-deplatforming. https://www.nytimes.com/2018/09/04/technology/alex-jones-inf... This type of reporting, plus my priors about how viral media spreads, inform my belief that deplatforming these individuals was moderately efficient for decreasing their reach. But it is an empirical question that would benefit from further study.