I too agree Lakshman would never follow adharm path like Vibhishan.
Yes , Ankita lakshman had said this dialogue because he knew that his brother Ram would never follow Adharm path so he respected his each decision .
This can be also proven by when Ram ask Sita agnipariksha and Sita maa second exile , he was the one who strictly opposed the decision .
For the first time in life he had shown anger and disapproval of Ram decision of Sita Agniparisksha bcoz he knew it is wrong to doubt Sita maa's purity.
Also as Shivam bhaiya said he also gone with Sita and on Sita order's he had to return back to Ayodhya to serve his brother Ram.
From this 2 incidents , it is proved that if Lakshman had borned as Ravan's brother then too he will only support right and dharm like Vibhishan had done. He would never supported Ravan , 😃
Hope I have clear your confusion dear Ankita !!! 😃😳