Certainly that would be a reasonable counter-argument, that the circumstances were such that he ought to have known. But that then invites a discussion about the exact nature of the circumstances Minsky was in. Personally I don't know what they were.

If those circumstances were unfavorable to him (as in your analogy), i'd be convinced that Minsky was at fault. If not, then I wouldn't be. But all that is to say that it seems to me that Stallman's abstract argument was fine to bring up - it just then puts the question back to his counterparts in the discussion to articulate a view on those circumstances to justify their position.