Lots of people made similar claims. Most notably The National Council for Civil Liberties (now called Liberty), the UK's leading civil/human rights organisation made submissions to parliament claiming that sex with minors was not always harmful, had a pro-paedo organisation as an affiliate and give them a representative on the gay rights subcommittee: https://www.thetimes.com/travel/destinations/uk-travel/scotl... The people involved were unaffected, some reaching fairly high political permissions.
A lot of other people whose works are respected have actually had sex with minors. Eric Gill and Oscar Wilde for example.
None of that makes Stallman's opinions defensible in my opinion. On the other hand I am happy to ignore his opinions on that topic and still value his opinions on other things.
> Through personal conversations in recent years, I've learned to understand how sex with a child can harm per psychologically. This changed my mind about the matter: I think adults should not do that.
https://stallman.org/archives/2019-sep-dec.html#14_September...