Libel isn't saying disagreeable things, it's knowingly lying about someone in a public context, such that it causes them harm.

It's not saying that you believe people of ethnicity X are inferior, or that gay folks and people who don't believe in your god are evil and deserve to die. It's saying, "John Doe is a child molesting, drug dealing, goat blower who's gonna steal all the shit from your apartment and tank your startup with his shitty code."

I can't see where there's value in society in allowing such speech.