With that said, Sumner did insult Butler's speaking ability.
If the Democrats wanted to "hit back" at Sumner, they could have insulted and ridiculed him in return (which they often did, according to what I've read).
There was no need to beat him nearly to death.
Adding to my last post...
What Brooks did was not self-defense. He was not defending Butler, either.
He attacked Sumner two days after Sumner’s speech. That was not self-defense. It was revenge. It was attempted murder because he beat him so badly, continuing to hit Sumner after Sumner fell unconscious.
The people of the South clearly thought there was. They lauded Brooks for doing it. I believe they put the head of his cane in a museum or something.
I think Sumner deserved a beating, though I think Brooks went too far.
I suspect the Southerners in the 1850s were hot headed and more willing to fight over insults than they are today.