The way you framed those two quotations is misleading to say the least. Clinton did not make that Tweet as a reply to Trump's tweet, his was from 2014, and hers was from 2016.
So, your statement, "Twitter isn't public discussion, unless you consider the following examples of discussion:", does not follow. You also say that "unless you consider" the aforementioned quotations to be public discussion, you therefore can not possibly view Twitter as a tool for public discussion, which is a false dilemma.
I agree with your last line though about Twitter being censored in a similar fashion to Facebook.
> The reigning attitude in physics has been “shut up and calculate”: solve the equations, and do not ask questions about what they mean.
Really? My physics teacher has taught me the exact opposite, that you must break away from relying on numbers and equations and approach every situation conceptually first.