Stop spreading lies, exact quote: "as long as we can counter them by rational argument and keep them in check by public opinion, suppression would certainly be unwise. But we should claim the right to suppress them if necessary even by force; for it may easily turn out that they are not prepared to meet us on the level of rational argument, but begin by denouncing all argument"

Important part: "But we should claim the right to suppress them if necessary even by force"

And there was no mention that the group were violent, just that they refused to listen. He mentioned that the group might get violent in the future not that they are, so we must strike them down preemptively.