I haven't even read it, so I believe I am the perfect person to fight you.
My impression, having not read it, is that these people want free speech without consequences. They want to be able to say hateful things and not be told they're hateful pieces of shite, or have their business/works be boycotted.
Seriously, I haven't read it.
But I have seen claims of people that signed it calling for someone else to be fired from their job for something they said on Twitter.
I get the feeling that at least some of the signatories are for their freedom of speech but not for those they don't like.