Requiring a unanimous vote to surrender early and a 4 to 1 vote to surrender after 20 is plain dumb and the cause of a lot of toxicity in my opinion.
Once three players on a team want to quit, they should be allowed to without anything else getting in their way. It is stupid to think that Riot is FORCING you to play a game that you, as well as the majority of your team, don't want to play anymore. Instead of your team simply taking this loss, moving on to a new game where you can start fresh and hopefully do better you are forced to play this losing game constantly anchored down and hindered by either your own failures or the failures of one or more of your teammates.
All this voting system does is give trolls ammunition to piss off and aggravate the entirety of their team. It's not even like other popular online multiplayer games where leaving is an option. Sure you can leave, but you can't load into another match before the one you are in ends, and even then you might get banned out for some unknown amount of time for leaving.
Once three people agree "yes, this game is screwed. Lets just give up" and then are forced to play more, their attitudes is going to go nowhere but down really fast, further increasing the probability of a loss. In addition to that, snowballing is very common, so usually if three people in a team agree to give up then there is probably no chance of coming back.
I know that this will result in a lot more surrenders, but that is perfectly acceptable if the player base can become less toxic because of it!