The thing is that this is game is largely dependent on cooperation for success. For example, imagine if you're playing a 5 on 5 game in basketball and you have one guy on your team that refuses to play defense so he stands on the sidelines when the other team has the ball.
You can see how your team would get frustrated as they either have to work harder to win or they're guaranteed to spend the next 30-40 minutes losing. Nobody likes to spend the next portion of their time knowing they're going to lose because of someone else's unwillingness to cooperate. That is why they're raging at you.
Like most of the others have said, most people that play this game derive their fun from winning and a lot of these arbitrary rules are more like all the trial and error that players have gone through to figure out what's the most optimal configuration for success especially when playing with people that have uncertain skill levels. A large portion of the player base already have a semblance of the 'strategy' involved with which characters are strong where and what builds go with which characters.
If you're looking for strategy it's more on the overall map control or the fine nuances of being more mechanically skilled than your lane opponent i.e lane control and harass regardless of the champ you're using.
Another thing is that the game really doesn't start till you hit lvl 30. At that point you have access to all summoner spells and masteries and even then, until you get the runes that you need you're technically at a disadvantage vs someone with all possible lvl 1 bonuses.