Before responding or even jumping to a conclusion, I want you to reflect on this question and truly evaluate yourself:
...Do you care if your opponent is having fun?
Sure, there are those of us who politely say, "Good luck; have fun" at the start of a match, but after that, is it really a consideration? If your dominating in your lane, do you stop and ask yourself, "Is my opponent having a good time?" If you successfully deny an opponent's play with your crowd-control and save your laning partner, do you think "I wonder if I'm taking away from their fun"?
I'm willing to admit: No, I don't. I don't care if my opponent is having fun. I care if _I_ am having fun. I won't be bitter about it if I'm not having fun, but it doesn't give me any solace either if my opponent is having a good time.
I say all that to say this: is it _my_ responsibility to see to it that my opponent has fun? To me, that's on them. And I suspect that, if people are honest with themselves, they generally feel the same way. Is it my fault that you're not having fun?
Despite all of this, the community seems to place a lot of importance on things being "unfun". Some people speak as if on some sort of "moral high ground" saying that things that feel unfun to the opponent shouldn't be in the game. I doubt these people give a second thought to the fun the opponent's having in their games, though.
If you truly, truly care if your opponent is having a good time, then I applaud you. But I also say it's not on you. It's every individual player's responsibility to make their own fun.