But we should claim the right to suppress them if necessary even by force
He then goes on, in the paragraph you quoted, to make it clear that it's refusing rational argument that's a problem because it can lead to violence, not violence itself.
Further, if you finish the paragraph it becomes clear that the opening statement is anything but a misunderstanding:
We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant. We should claim that any movement preaching intolerance places itself outside the law and we should consider incitement to intolerance and persecution as criminal, in the same way as we should consider incitement to murder, or to kidnapping, or to the revival of the slave trade, as criminal.
You don't have to agree with him, you can be partial to rawles, but popper was not vague.
