Your argument falls apart when one notices your premise relies upon two things:
1) that the toxic behavior is both justifiable and triggered by other players' actions
2) that the toxic behavior is fun
The first simply isn't true. If someone plays badly, that sucks. That doesn't give other players permission to give them shit about it. There's a reason curbstomping someone who got the last doughnut you wanted is illegal: being mad at someone doesn't give you the right to take it out on them.
The second might be true, but if you have to ruin my fun by being an asshole, that's you being selfish. I'm just trying to play the game. Fortunately, that's why blocking chat from other players is an option. =D
And, of course, all of the above can be cast aside when you recognize that 90% of the time the guys being the most vile at any given time are very likely not the ones playing the best on either team, which removes even the illusion of "righteousness" behind their jerkass behavior.
@Zefie: I'm not siding with anyone. I couldn't care less about the whole Frejlord thing despite Ashe and Anivia being two of my favorite champions and my first purchases in the game. The lore has literally zero presence in the gameplay so I ignore it; it doesn't add anything for me.
You're right, partly. Toxic behaviour isn't justifiable. There's no permission slip that your mother has to sign to allow you to be a toxic player. However, I simply don't need to be justified if I want to be toxic. Not being justified is not going to stop a winning top lane to bitch about his or her teammates. Again, as I said before, I'm not referring to the players who are toxic for no reason; that is, those that do bad and still talk shit to his or her teammates. Whether or not toxicity helps the team is another issue, but if you don't understand my reason for being toxic, then it doesn't mean I don't have reason to be toxic.
As I said on the previous page, "there's nothing wrong with toxic players as long as they can carry."
I find nothing wrong with toxic players as long as they have the skills to back it up. That's just my personal opinion. If you want to talk shit, you better have a pooper scooper to clean yourself up. Otherwise, it's just embarrassing.
On the previous page, a lot of you didn't agree with what I said about toxic players and how they don't matter. You guys are obviously just in lane and taking the verbal abuse even though no one's forcing you to suffer through any of it. My solution to the excessive toxicity directed at you or your teammates: the block function.
You're spot on about the selfish bit though. It does go both ways. However, I merely said that it was the baddie that initiates the toxicity. No baddie, very likely no toxicity. No toxicity, very likely still baddie. I think I wasn't very clear about that whole last bit, how I actually APOLOGIZE when I'm doing bad and being called bad. Apologizing usually ends any problems of toxicity, even if you're insincere about it. Retaliating and not showing remorse will only further toxicity, usually. Exceptions to rules, always.
tldr; No rights/permission/justification involved with toxicity. Toxicity okay in my books; just don't embarrass yourself by playing bad. Order of events: baddies -> fun ruined -> toxicity ensues.