if I was out with my friends/family and I fell in a river (btw I can't swim v well) they would probably laugh at me, then help me out. Okay, so they don't hate me, but what I'm trying to say is that just because they laughed at me, doesn't mean that they want me to drown, or that they are sadists.
We could see how concerned Karthik when Survi was crossing the bridge, he was really tense.
So maybe he enjoyed seeing her flail around like an octopus for a bit😆but how could he allow himself to show concern, by shouting out for her and all that jazz. He can't intentionally show any thing else but hatred for Survi. When she began to sink under her rescued her. I don't know what his thought process was, but nafrat or not he couldn't let her die.
Karthik has never had any intention of killing Survi. He's said he's wanted to make her into a living corpse, just like what happened to his mother, but if he had any intention of actually hurting her he would've done it long ago, he's had plenty of chances.
My personal theory is that he couldn't let Survi leave him again. Even if she's struggling, or in pain, it's fine as long as she is in his sight. But won't let her disappear again, he can't bear to.
He couldn't let her drown that day, even with revenge in mind, because that would mean she would be gone forever.
In this entire post I've probably just stated the obvious, but I do think it's quite an interesting topic to discuss.