Freedom of Speech allows us to share our opinions, including those that are offensive to others, as long as we avoid force, fraud, or defamation.
So why is it that some groups are allowed to restrict speech and others are not?
We don’t allow the government to restrict speech because it doesn’t have any competitors. It could stamp out all disagreement, leaving no room for opposing views.
In general though, private groups are allowed to restrict speech, membership, and other activities on their own property because there are many other options available to people.
Thus, universities can set whatever speech codes they like, because students are always free to go elsewhere if they don’t like the restrictions.
When people aren’t prevented from saying what they want to say, it allows for every view to be heard, without compelling anyone to host or pay for speech they disagree with.
So, monopolies like the government are not allowed to pick who speaks and who doesn’t, but organizations that face competition are free to do so.