IANAL, and this is not legal advice, but I am surprised at the FSF's view here. I believed (and believe) that copyright requires a substantive change to form a derivative work, and I would rather doubt that changing the comments counts. (Now, I think that precedents in the court have set the bar for "substantive" pretty low, but not that low.)

I would also say that "legal" is not always the same as "ethical", particularly in this circumstance.