Most of the ones I have seen get kicked off of Free Republic have been booted for posting lying articles, engaging in personal attacks, and otherwise breaking rules. Not because they were leftist. For the Record, Skinner, Will Pitt, and Bev Harris all have Free Republic accounts that have not been banned.
Further, Free Republic does not engage in IP banning, grants instant access, and one E-mail account can have multiple user names. Compare that to Democratic Undergrounds uncertain and flexible rules for banning, IP blocks, e-mail blocks, and 24-hour account sign up holds (one can presume that some form of screening occurs during this time). One can reasonably assume Jim Robinson fears free speech a great deal less than Skinner does.