Why, so many trolls?

In my past 6-7 games I've had at least 1-3 people saying their gonna troll or feed enemy team in the chat before the game even starts. While we are still picking champs out of no where they just start laughing saying I'm gonna troll. Yet when one of my friends or me leaves that game before it even starts, while we are in champion select we have to have a wait time and get in trouble. Just because i don't want to sit threw a 20-60min game of losing just because a few people want to troll because they think its funny yet the rest of us have to either get in trouble for it or sit threw a horrible game just because we don't want get in more trouble leaving a game that has started. The system is stupid and needs to be changed. People should be able to leave a losing match or be able to find a new game when their own teammates literally starts saying "I'm trolling, or I'm feeding". I'm ready to quite playing league for good and join everyone else on Overwatch or something else that prevents that by letting us leave unranked game modes. I can't take it anymore league is full of trolls and toxic players.