It absolutely goes against what the spawn ending is supposed to represent and this adds fuel to the fire as well:
Originally Posted by Ametris
That dialogue is pure cringe and totally makes him feel more insecure. It's in even poorer taste if we take into account what Cazador says about Tav if they go meet him without Astarion. He compares Tav to himself (an equal influence - basicly Astarion's temporary, alternative and kinder master) and implies that Astarion doesn't know how to be on his own and that he basicly needs someone above him.
It's terrible.
And I agree, I clicked on it once, was not surprised by his response at all. There is only one option for us to choose and THIS is what we end up with? Feels like Astarion's dialogue till his last lines about Cazador saying how he's free and him and Tav are equals was written by one person and this one dialogue including the scene at the docks was written by somebody else entirely.
It's as if they paid less attention to his good ending compared to the evil one..