Erm, it's not empty and they 'grey out' the button if you remove all the text. 

![enter image description here][1]

I guess it's an attempt to get people to leave a constructive comment but as ever 'pink and fuffyness' prevails and you're not forced to do so.

To be honest I frequently find it difficult not to 

    s/about/a steaming pile of shit./

so I go with 

    s/ about/./


  [1]: https://i.sstatic.net/kck5t.png