“The standard of proof for an affirmative defense is “preponderance of the evidence” not clear and convincing and not beyond a reasonable doubt. He merely has to show that it is more likely than not that this was self-defense.”
WRONG! Wisconsin statute:
(3) Burden of proof. When the existence of an affirmative defense under sub. (2) has been placed in issue by the trial evidence, the state must prove beyond a reasonable doubt that the facts constituting the defense did not exist in order to sustain a finding of guilt under sub. (1).
IOW it has to be placed at issue by trial evidence. The defendant has to provide actual evidence that he has that defense. Once he establishes evidence supporting the defence, the burden shifts to the prosecution and becomes "beyond a reasonable doubt."
The prosecution does not need to disprove all affirmative defenses, only the one's supported by the defendant with admissible evidence.