We have Safe Spaces here on DU. They are called Groups.

We also have public spaces on DU. They are called Forums.

For any group to want to have a safe space is not a limitation on freedom of speech, other than in a particular locale at a particular time, but does provide a space for those of like mind or interest to congregate and discuss what is important to them, without interference. This has value in building a community with similar beliefs and interests. It also has value in strengthening minority viewpoints where they can be drowned out by majority viewpoints.

There are plenty of other spaces to have complete freedom of speech about the same topics where all can be challenged. There is great value in both safe spaces and open spaces. Safe spaces are no threat to total freedom of speech, because of the prevalence of open spaces.

DU, on a Meta level, is a safe space. Republican viewpoints are not allowed here. It is not a totally open forum, and that is OK.