The public square was an important tool of democracy in days past because it provided a forum for disparate citizens to discuss the important issues of the day.
Conclusion (hence)
We should ensure that Internet users have at least as much freedom of expression as did people speaking in the public square.
Evidence
The public square was an important tool of democracy, because it provided a forum for varied citizens to discuss important issues of the day, and now the Internet plays the role of the public square.
Evaluate
The conclusion is making a recommendation ("should"). Does the evidence define what we should do or have anything normative or evaluative that would match that concept?
It sounds like the author places value on the public square, saying it was an important tool of democracy.
So if the author is concluding that we should ensure that Internet users have as much freedom of expression as people did in the public square, she must be thinking that freedom of expression is an important part of having the Internet play the same role as the public square did.
Maybe she's assuming .
There's also a wrinkle in this argument in the sense that the author says, . But do Internet users need the Internet to play that role? Or do they have other options for something that could play the role once played by the public square, in which case we don't need to specifically make sure that the Internet is ready to play the role?
Does society even need that role to be played? The author seems to assume that we should do what we need to do to make sure something modern can play the role of this "important tool of democracy". What if we're done with democracy?
Goal
This argument does not lend itself to an obvious prephrase. We know broadly that the author cares about maintaining the important democratic tool of providing a forum for disparate citizens to debate modern issues. And we know that she thinks that for the Internet to be this tool, we should be making sure people have at least as much freedom of expression as they did speaking in the public square.