Gosh, why it's so hard to hammer the point in this community? Ok, listen: the issue starts from Judge's believes, Judge isn't against kindness for sake of brutality or heartlessness, Judge believes that a
HUMAN being cannot become
STRONG with
EMOTIONS. Judge's ONLY issue with
EMOTIONS is because of that believe, he doesn't have anything else against emotions or kindness, he just thinks that the Vinsmoke Dynasty cannot become strong with emotions, that's it. I hope I was able to explain this part...
Now, Sanji as Judge's ONLY child that has his emotions intact, had the opportunity to change his father's beliefs by not relying to his thecnolagy but rather to his KINDNESS to become stronger, why? Because humans' driving force is their
LOVE AND COMPASSION towards each other. We, as HUMANS, are at our best when we fight for those we truly love. You know what would be an incredibly strong and memorable moment? If Sanji did something incredible in WCI and Judge asked "Sanji, tell me, why are you so strong? Where does your power come from?" And Sanji says only one word "Love" that would be the most powerful thing that Oda would have ever done, but unfortunately he didn't do that. Now we have a situation where Judge ended up being right.