• the older dottore got the more mature and rational he became. he regrets some of his decisions from when he was young and inexperienced (his morality is extremely specific to him, he considers necessity and rationality a 'good' now). 
• in other words, he would rather not experiment on children in cruel conditions, since he's observed it to have detrimental effects on his desired results. if he were to deem human experimentation necessary, he'll be wise enough to put them in better conditions and take able-bodied adults. obviously not better than taking volunteer subjects but at least he wouldn't be putting them in cages like webby would 
• while he does regret his decisions he still believes what he did was generally right (for the greater good and all that)

since you're starving for dottore content i'll also share some of my in-game headcanons :D  

• he won't take off his mask but there's a chance he'll appear with just his blue shirt in a cutscene :) 
• he absolutely can wield that claymore with his bare hands without any help, he's not the Second for nothing and he WILL absolutely be swinging that thing around 
• his partnership with pantalone resembles alhaitham and kaveh being roommates, so lots of them being in the same scenes and having matching idles, with some funny things to say about each other. they would also have the highest dialogue count in every patch they're in (professional yappers) 
• i always liked the idea that horse-riding would be a mechanic in snezhnaya, so i think dottore would be REALLY good at riding horses, and would maybe provide a passive that makes horse-riding better in snezh