Okay, so the librarian is clearly in the wrong as this is a classic case of viewpoint discrimination. I know that some of the right will want him fired. But I think that is a mistake. It will be the type of cancel culture they complain about. What I would want is for him to have to go to first amendment training. If he still persists in doing stuff like then yes fire him.
And I want the group to get their room back and do their program. They will get some publicity for this which will make up for the loss of their time on their first attempt to do the program.
That is a way of handling this that shows grace and cements the importance of first amendment rights. I think given the polarization in our society the more grace we can give each other the better off we will be.