You are absolutely right. However is it possible, to not flame in some circumstances?
Like seriously now 3 days ago i went duo with a friend of mines. And the games were absolutely horrible (quality wise). I had 2 or 3 games in line (im not sure how to phrase that in english) where my junglers literally ignored my lane.
The first that comes to my mind is the garen (me) vs illaoi,top. I leashed his red and tanked for him. I came to lane with 3/4 of my hp. I ended up falling behind in exp and gold because apparantly illaoi with w at 1 lvl is pure cancer. She pushed throughout the whole laning phase and twitch didnt gank even once. I asked him (kindly ofc, until he outright ignored me) to come and help me. He didnt come.
Another i remember was with a fizz vs orianna. Said orianna had also barrier so me killing her solo would be difficult. I asked my jungler kayn to gank me because orianna was pushing trying to poke me, but he never did. I had fallen so behind that after 6 i couldnt kill her even if i landed my ulti from long range.
There was also another game where i was i think fizz vs ahri. I asked my jungler kha to gank her before she hits 6 and becomes a pain in the arse to gank. Spoiler alert...... he ganked! 10 seconds after ahri hit lvl 6. I used my ulti to maybe force hers, and i did. Still she had 2 more dashes to avoid kha (lvl 5 i think). Fast forward some mins ahead and she bullies me hard and i have 0 ganks, i told him to come and gank her since i can burn her ulti. But he didnt respond or even pay attention to my requests. I ended up abandoning my lane (i couldnt farm under turret without losing 45%+ of my hp) and just went to roam. Needless to say we lost and my team even blamed me xD.
Oh yeah my favourite. I had kog maw jungle, in ranked. Where he didnt gank anyone and served as a gold sack for the enemy.
Anyway my comment devolved in a rant, but my point is that riot really doesnt do anything to help you avoid flaming. They dont try to correct the root of the problem because they deem it "impossible" which really is not. It can take time and resources but its definitely not impossible.
Edit: Oke i think i was a bit misunderstood. I dont want to support flaming. I just wanted to give insight as to why flaming is a thing. And why "holding back" sometimes it just doesnt work.