I don't think even the danafor bit is THAT relevant in that regard. We saw bits and bits of it... Meliodas apparently blew up the place after people were already dead. So even that extreme scenario doesn't evidence meliodas being so lost in his rage that he is a risk to others. Now, merlin did not know that of course and it might even be reasonable for merlin to do this from her perspective but that also has several negative implications:He really should've portrayed Mel as he was during those Danafor flashbacks when it was clear he was losing control of the PoD within him or made it look like he was about to enter Assault Mode. Here it just looks like regular angry Mel and it looks like Merlin jumped the gun on knocking him out.
The first would be the that meliodas and merlin simply never talked about what happened at danafor. The sin's lack of communication is a shit pile which keeps getting bigger and more toxic which is something which this series simply did not need.
The second is that if we assume meliodas and merlin did communicate, this ends up looking like a huge and contrived blunder which she based on basically nothing. And this is considering that merlin is basically the person that knows meliodas the best AND for the longest. Because she was a surrogate daughter for meliodas back in the day and unlike elizabeth has had a single uninterrupted life since then.
The third is that mel's reaction here is straight up uncharacteristic of him. At least we know him.
Now, meliodas using his more advanced demon mark at that point IS worrisome. We are talking about a dark power that awakened by sheer anger. Meliodas blowing up liones probably was not going to be a thing but mel's heart being corrupted and hurting others was plausible. But the issue here is... meliodas does not seem to be the type to be angered over so little. We saw him back during the war where he even used his advanced demon mark and he didn't seem particularly murderous. So his reaction here seemed like an exaggeration on his part. It was just an unintentional scratch that elizabeth got. AND there was no reason for him to think someone was trying to separate them.
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