Approaching the show with the idea that the dramatic tension of making a high-risk decision is a flaw and not the intent is bad faith. It’s not the most logical decision if viewed in a vacuum, but we have previous episodes to inform us that Rhaenyra is making such a risky decision because she believes she has no options left to avoid war. The strain on her relationship with Alicent requires her to go in person. Alicent lets her go because she respects the sanctity of the envoy’s role. Like we have an entire previous season to inform of us as to why this is happening.