After the Diet of Worms, Luther had to find a place where he would be out of harms way. A Prince close to Luther took him away to Wartburg. He was safe physically, but not emotionally; for while there, he could not defend his ideas and it hurt and angered Luther more than a dagger ever could.
While Luther was away, Andreas Bodenstein von Karlstadt (famous for changes in the church) and Thomas Muntzer took it upon themselves to be the new leaders of the reformation.
Karlstadt was a lot like Luther; he shared some of the same ideas, and was also a professor at Whittenburg. Muntzer learned a lot from Luther and at first looked up to him as well. However, these kind things didn't last very long.
Luther criticized both these men because of the new ways they where teaching. In Luther's letter "Opposition of the Fanatic Spirit" he states, "These prophets have little sympathy, taste, or understanding"; "They...want
people to be amazed at their great skill". It seems that he feels Karlstadt is only in it for the glory of himself and because of it "Christ is forgotten".
Luther is not any more pleasant in his critiquing of Muntzer. In his letter to the "Princes of Saxony concerning the rebellious Spirit", he mentions that Muntzer wants to, "enforce faith in an immediate and dictatorial manner". It's obvious Luther doesn't agree with this tactic.
I think that it's easy to say that both Karlstadt and Muntzer would want to respond to the criticism and have people listen; however, being the popular man Luther already was made it tough for them to get through to the more important people. For example, Luther's letters stated above probably had more people follow his word then Muntzer's rebuttal...