There are definitely some scenarios where you'd want to restrict the labeling of content (think: labels on official policies where the user has no right to comment).
However, the problem is not as bad as it seems because if the user does not have edit rights on the space then they can only add personal labels. By definition, no one else can see them.
No, you can't limit the creation of labels. The whole point of them is that people can enter arbitrary text.
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