This is an... intriguing... effort. "Liberalism unrelinquished", organized by Kevin Frei and Daniel Klein.
"Political language -- and with variations this is true of all political parties, from Conservatives to Anarchists -- is designed to make lies sound truthful and murder respectable, and to give an appearance of solidity to pure wind." - Orwell, 1946
I know it can be tacky to use this essay of Orwell's to criticize people. But what else are we really to make of this? It is an effort to manipulate language to purge political opponents out of respectability (if they are not liberals presumably they have an illiberal perspective?) and to obscure the liberal tradition in order to align it with more specific political ends of the signatories. I don't think it's particularly dangerous (or that it will be effective) but it's not encouraging to see either.