LOS ANGELES >> Ashton Kutcher has resigned as chairman of the board of an anti-child sex abuse organization that he co-founded, after he and wife Mila Kunis wrote letters seeking leniency for their former “That ’70s Show” co-star and convicted rapist, Danny Masterson.

Kutcher stepped down from the board of Thorn, an organization he founded with then-wife Demi Moore in 2009, on Thursday, the group said in a statement.

“After my wife and I spent several days of listening, personal reflection, learning, and conversations with survivors and the employees and leadership at Thorn, I have determined the responsible thing for me to do is resign as Chairman of the Board, effectively immediately,” Kutcher wrote in a letter to the board. “I cannot allow my error in judgment to distract from our efforts and the children we serve.”

A Los Angeles judge sentenced Masterson to 30 years to life in prison on Sept. 7. The actor was convicted in May of raping two women in 2003, when he was starring on the Fox retro sitcom “That ’70s Show” with Kutcher and Kunis.

The day after the sentencing, letters to the judge from Kutcher, Kunis and many others were made public. In Kutcher’s, he called Masterson a man who in his experience had treated people “with decency, equality, and generosity.”

Kutcher and Kunis apologized the next day in an Instagram video for writing the letters, which Kutcher said “were intended for the judge to read and not to undermine the testimony of the victims or retraumatize them in any way.”

Kutcher said in his resignation letter, first reported by Time magazine, that he offered “my heartfelt apology to all victims of sexual violence and everyone at Thorn who I hurt by what I did.”