Sure, it is very easy and convenient to allow dissent only when it offers no risk. But if there were a chance for them to became popular, then FBI would restar

Sure, it is very easy and convenient to allow dissent only when it offers no risk. But if there were a chance for them to became popular, then FBI would restart the pogroms from McCarthyist era. There are still Black Panther members jailed and kept in solitary confinement because authorities are afraid that they could talk with other inmates and convince them of their ideology.