Without RMS most of the software you are currently using wouldn't work. He has orthodox manners and is an extremist for freedom but "terrible harm" is a lie.
What makes you think someone else would not step in instead?
There was a similar argument when Ritchie died: "we would not have C, we would not have software". Well, maybe we would not have C, but for sure we would have (and already had) some other programming languages.
Sure, "copy-center" attitudes like those common in BSD communities would have prevailed, likely, and we'd have entered the shared-source/commons-licensing phase a decade earlier. Without the option of copyleft, an entire pillar of philosophy would be missing, but it likely would not matter, since the world would still be just as corporatist. The main thing missing in that world would be a belief that copyright can and will be changed in order to better suit the people.
I think you underestimate the impact of GNU on your daily life. Sure, someone else might have made the same things, but in this timeline RMS did and by removing him, most of the software you are currently using falls apart.
From what I hear, it was actually RMS who originally convinced the BSD people to release their software, i.e. to create the BSD licence. I can’t remember where I read this, though, and I can’t find it now.