Alex Payne founded a socialist blog: https://www.jacobinmag.com/ Why is writing about certain political ideas OK, but writing about certain other political ideas not OK? Why are those certain other political ideas "not OK" enough for someone to be banned from a technology conference?
Imagine you lived in soviet Russia. If you criticize the communist government, and said that the previous capitalist system was better, you would be shot. But if you criticize the government and said we needed more communism, you'd get praise.
If you are in favor of reform, and new policies, and support the direction society is currently headed, you won't be ostracized. People might not agree with you, but they won't have you shot.
But imagine trying to suggest we go back and undo the changes that have been made? Imagine someone advocated reestablishing slavery, or getting rid of women's right to vote, etc. They would be ostracized.
You might not agree with the person who wants to create a new system. But the person advocating we go back to the old system, no. He's trying to undo all the progress we've made!
Society has fought that battle and established that the losing side was wrong. It may have been controversial at one time, but now everyone knows that slavery is definitely wrong. The liberal isn't fighting lost wars, he's moving onto new battles. Where no one has yet been declared a loser.