“Believe me, it is not failing to speak out with promptitude and energy that is the matter with you; it is having nothing consistent or valuable to say.”

He must be talking about politicians, the media, and lawyers. Dazzle them with bullshit.

I here ditto Archer

Another way of saying "It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt", as I think Mark Twain said.., although Arnold may have said it first, as he was a few years older

A foolish consistency is the hobgoblin of little minds. ---Ralph Waldo Emerson

As it is written:

" For out of the abundance of the heart, the mouth speaketh."