Statements made by Rengar Players + Evidence that Rengar is a proxy for psychopathic expression.
"It's fun once you have the instaburst combo down pat. You're pressing the same buttons each time but seeing the ADC cry in /all because you 100-0'd him before he could react never gets old". - This statement is basically saying that the champion itself has no value. A summary of this satement might be phrased as, "He is fun after you figure out how to make someone have a bad day".
"Besides, rengar gets fun after you get fed and then you force the enemy team to play like bitches the rest of the game or else they die". -Shows that fun with Rengar centers around feelings of power and sadistic gratification
"Also there are some people like me who do enjoy playing him"-shows that rengar players are cognizant of the fact that the enjoyment they get out of the champion is different from that which a normal human being would get.
"as rengar when ulting, i just like to stalk people until near the end of it's duration, then kill. Pretty hilarious seeing them freakout by the mark"-A specific example of sadism and the gratification received by the rengar player. Note that the satisfaction mentioned is coming from the discomfort and fear of another human being. Not from playing skillfully. This is exactly the definition of sadism.
From a game development standpoint, I think that if you accept my arguments and evidence then continued support of this champion and his playstyle is unethical.