He spends a lot of time discussing why pedophilia isn't rape.
Of a woman having sex with a minor, he said “I wish an attractive woman had ‘abused’ me that way when I was 14.” He directly addressed child pornography by saying that “making such photos should be a crime, and is a crime, but that is no reason to prohibit possessing copies of the photos.” He defended pedophilia, in general, in saying that “there is little evidence to justify the widespread assumption that willing participation in pedophilia hurts children.”
I mean, in a very technical and probably unintentional way, he is right. Paedophilia is, principally, "only" the sexual attraction to minors. That does not necessarily imply actual molesting or abuse of children. And not all who molest and abuse minors are paedophiles. It might just be a matter of power/sexual repression (looking at you, clergymen). Equating the two is probably a hindrance to those struggling with these feelings coming forward and seeking psychiatric help (like drug criminalization).
As for whether or not it is rape if an adult person has sex with a horny teenager... Maybe I wouldn't call it "rape", but there's also a reason we don't let kids sign contracts or drive cars.
He got some heat in 2019 after an untastful statement he made regarding the Epstein case. A massive backlash happend, followed by him leaving many of his positions, esp. at MIT and at the FSF. Eventually he made some public excuses and got re-integrated to the FSF board, to the displeasure of some.
To elaborate after I Googled to find more information about this:
Stallman had cast doubt upon the reports that AI pioneer Marvin Minsky had sexually assaulted one of Epstein’s victims. In an email chain sent to the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) mailing list that was published by Motherboard, Stallman said that “the most plausible scenario” was that Epstein’s victim “presented herself to [Marvin Minsky] as entirely willing.”
Stallman also described the distinction between a 17 or 18 year old victim as a “minor” detail, and suggested that it was an “injustice” to refer to it as a “sexual assault.”
and a different article:
Virginia Roberts Giuffre, a victim of Epstein at age 17, testified in a May 2016 deposition that "she was directed to have sex with Minsky when he visited Epstein's compound in the US Virgin Islands,"
Stallman objected to the text of the event announcement, saying that it "does an injustice to Marvin Minsky" by saying that Minsky was "accused of assaulting one of Epstein's victims."
"The word 'assaulting' presumes that he applied force or violence, in some unspecified way, but the article itself did say no such thing. Only that they had sex," Stallman wrote.
Stallman added that "the most plausible scenario is she presented herself to [Minsky] as entirely willing. Assuming she was being coerced by Epstein, he would have had every reason to conceal that from most of his associates."
After one person wrote that "Giuffre was 17 at the time; this makes it rape in the Virgin Islands," Stallman responded, "I think it is morally absurd to define 'rape' in a way that depends on minor details such as which country it was in or whether the victim was 18 years old or 17."
"We know that Giuffre was being coerced into sex—by Epstein," Stallman also wrote. "She was being harmed. But the details do affect whether, and to what extent, Minsky was responsible for that."
"Headlines say that I defended Epstein," Stallman wrote. "Nothing could be further from the truth. I've called him a 'serial rapist', and said he deserved to be imprisoned. But many people now believe I defended him—and other inaccurate claims—and feel a real hurt because of what they believe I said. I'm sorry for that hurt. I wish I could have prevented the misunderstanding."
Stallman, who in 2006 wrote, "I am skeptical of the claim that voluntarily [sic] pedophilia harms children," also wrote in September 2019 that he had changed his mind about sex between adults and children.
"Many years ago I posted that I could not see anything wrong about sex between an adult and a child, if the child accepted it," Stallman wrote. "Through personal conversations in recent years, I've learned to understand how sex with a child can harm per [sic] psychologically. This changed my mind about the matter: I think adults should not do that. I am grateful for the conversations that enabled me to understand why."