But I'm not convinced the folks on Twitter truly have that much power because they have those discussions on Twitter (and most would probably have that power whether Twitter exists or not and the discussions on Twitter from those in power seem to be mostly just an extension of their other media presences). It does make some folks more accessible, and their (curated) thoughts more public in some cases.
I've spent some time recently to curate who/what I follow on Twitter to be more relevant and less hysterical (it still creeps in tho), and that has actually made me more likely to actually engage there now, as it's often with things I'm actually interested in.
And what exactly are you afraid of, someone judging you by what you say?
IDK, that sounds like more participation (in speaking and listening) than I'd expect out of a literal public square, although not by a whole lot.
I remember coming across street preachers on the Santa Monica promenade. I want to say 10-20 people would stop to listen, where 1-2 people would be speaking (preacher and a possible commenter). I don't even know how to estimate how many people simply walked by, but the audience being less than 20% of that sounds very likely.
TL;DR Anecdotal experience in one actual public square, estimates less than 20% of the physically present public participating, and less than 10% of that speaking.