By design the Forums Filtered By Label Page displays a list of forum contents using the label selected; it is not designed or intended to start a discussion - the same reason why customizing and adding primary-post-button did not render the component effective.
Nonetheless, it appears like a promising Product Enhancement. On similar lines, it is an earnest request to raise this concern by posting about it in Khoros Product Idea.
I hope that helps. 🙂
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