We don't expect to just be able to start a random game with untrusted strangers in real life and be assured they're not going to cheat.
Could you imagine if any time you wanted to play sports in real life you had to consent to wearing something that could read your mind so that it could determine you weren't cheating? That seems as ridiculous as the end-game of client-side cheat prevention.
I understand there are competitive settings where money is involved and that's where you need referrees. Otherwise, I think we've gone down this road where we take cheating far, far too seriously. I say this as someone that absolutely loves videogames, so I'm not meaning to disregard them.
Trusting strangers is ultimately a problem you'll never solve completely. I just don't think there's a technical solution to it.
Also, far out I hate some of the big companies in gaming. The attitude that Riot is displaying here just sucks.