The name "Katzer" ... (Information on the distribution of the name "Katzer" in Germany is available here)
Franz Gerhard Soural told us that his late aunt had mentioned in her family chronicle that the Czechs spelled the name "Kadcera"
Another interesting explanation is the alteration of vowel sound from "e" to "a", which was quite common in the Silesian dialect (e.g.das Herz = doas Harze or Klecks = Klacks). It would make the change from "Ketzer" to "Katzer" very likely
According to the German Brockhaus Encyclopedia
the word "Ketzer" has developed from the term "Katharer" (i.e.
Catharist). It referred to a heretic who had diverged from the
Cathari (Greek: "the pure ones") was the name of a religious movement invading Europe from the Balkans at the beginning of the 12th century. They quickly found supporters in the Rhineland, Northern and Southern France, England and Northern Italy. Not much later the church initiated counteractions that lead to bloody persecutions of the Cathari. "Ketzer" may, of course, also refer to any outragous person. Katzers have obviously never been well adapted people.
The theory of the name relationship ' Ketzer-Katzer' is also supported by a report in the historic chronicle "Neue Kronik von Böhmen" dated 1780 (page 116): The complete chronicle can be read in Google Books. The Book is only available in German, though.
A German dictionary of family names (Duden der Familiennamen) offers additional explanations:
The same dictionary also mentions several derivations of the initial part of the name: "Katz":