It was used against the GPL back when the GPL first came out. RMS wasn't convinced by it then, why would he be convinced by it now?

Besides you're way overestimating the impact. Take a GPLed tool like emacs. If you write code with emacs, the code that you've written is yours and you can do with it what you want. Likewise if you write a website with emacs, by no stretch of the imagination can that website be viewed as a public performance of emacs. Therefore you'd be unaffected by the change.

However if you were using, say, a GPLed library for dealing with XMLhttpd requests, then the public website which is delivering data to clients using that library might be considered a public performance of that library. (This is assuming that a court rules that this is public performance, which is a question that no court as yet has considered.) And then you might have extra clauses to consider.

Cheers,
Ben