When Did Having Skill Become an Excuse to be Toxic?

I played ranked today, and was 2nd pick. I locked in and said "mid", since no one had called it. All is well right? 5th pick locks in , and types "mid". Uncalled for, but okay, I'll be the bigger man and go top. (Against by the way who dominates .) The game starts and of course our team is mad at , "report after the game", "negative attitude", "toxic" etc. I go top, and lose. I'm 1-4. He goes mid and wins, he's 3-1. We eventually lose the game. No one on our team did well except . Then, in the post-game lobby, all of the sudden, my team starts raging at me? They're saying I'm the reason we lost, I fed, and since did well and I didn't, no one wants to report anymore, and now my team wants to report me for losing lane. (Neither I or typed barely anything in game)

Why is this allowed? I wasn't aware that being toxic was OK as long as you did well in-game? Is that really the mindset of some people? No one even cared about what he did after the game, since he did decently in game. Is winning ranked and gaining LP more important than having fun and playing with teammates who cooperate? This game today only reminded me of why ranked is far less enjoyable than normals games. I feel like people get blinded by the sight of those precious LP gains and care about nothing other than winning. I understand, sure, ranked is for trying your best, and winning. But at what cost?