Why is the community so toxic?

Ok so I've had a run of a few bad games since the patch. Yorick - who I wanted to main - doesn't feel as 'pokey' with the latest, more expensive items so the game has sort of demanded that I move on to find another champion I like by making him a little more obsolete than he was starting to become already. That's fine. I can deal with that. I'm a lv11 summoner and I started playing semi-seriously last week, though I have had this account for a while because I was a casual, on and off player a long while ago now.

New champions means a teething period for me where I find a good balance and feel for how different items will directly affect him/her, and as such I will generally have a few bad games. I can accept this.

Why do I only get hate and flame spewed at me when all I wanna do is play a game where, if the other players aren't happy with my performance, advice could be offered?

Even after the match I will still get private messages sent to me that are just filled with poison, and why does Riot allow players to report others as having a "low level of skill"? Surely that just fuels everything that's wrong with League of Legends and promotes a sickening level of competitiveness?

My last few losses, around the 18 minute mark, my score has been at 0/0/0 and I still have all towers in my lane and I'll probably be the last one to lose a tower in lane. But the minute I misstep and make a mistake and an enemy gets that initial kill on me, it'll all go to hell and we'll lose. It'll be my fault. I'm sick of it. I don't want a community like this.