Alright so I've been reported in the past for verbal abuse. I get the whole idea, but there is two things that can stop anyone from verbally harrassing you. One, turn on language filter. Two, Mute them. So pretty simple right? So why make it a reportable offense?
Second question. When is it okay to harass players? Like for example if someone is trolling or feeding? is it okay to get mad? 
inb4 salty.
Godhri4 votesVerbal abuse like any abuse is never justified. Despite it being possible to mute and language filter abusers, the whole point is that we shouldn't have to. It is a reportable offense because Riot along with many other league players want a civilized and likeable gaming community.
As for your second question, like I said above, it is never justified. You can get mad but that doesn't mean you have to flame them. No one is saying you can't get mad, but you can and will be held responsible for what actions you take when you do get mad. Being mad isn't a reasonable excuse for flaming behavior. There are ways to handle a situation without flaming and Riot wants to promote those ways as flaming tends to beget flaming and it mostly just escalates a situation.
Of course, as I don't work for or represent Riot, this is just speculation on my part.
LilMsCantBeWrong2 votesTwo wrongs don't make a right.
WyvernEgg3 votesTwo wrongs could make a right. But you would still have two wrongs.
Hinro Honato2 votesSure, flame all you want. Enjoy the ban.
Raptamei2 votesTrolls are trying to make you mad.
So no, getting mad at them is not useful.
SmknWdl1 votesIt is ok to be mad, frustrated, etc. But we're behind computer screens. It's not face to face. You have the option to just not say anything. Flaming always give the troll what they want to see, a reaction. So it's better to ignore and play the game.
OkayTrash1 votesRiot wants to promote all this but has an option for you to mute, and turn off language filter. Seems like they are okay with people using "vulgar" language. I mean I'm probably the minority but it honestly pisses me off when you waste my time. I work full time I would enjoy to play a game without a 12yr that gets butt hurt. If I've insulted someone they generally deserve it one way or another. I just don't see anyway of fixing the problem of idiots? I always think maybe if I guilt trip them into doing something they may change.
Godhri1 votesSo your excuse for flaming someone who may not know any better is that you work full time and want to enjoy a game and part of enjoying a game is being able to put someone down for their incompetence without consequence.
Interesting. I see your point about wanting to enjoy the game but it really doesn't justify putting someone down or flaming them.
By the way, I'm not saying I'm perfect. I am definitely guilty of slipping up occasionally and flaming people but I never try to justify it with anything.
I also don't see your point that you were trying to make with your first sentence.
OkayTrash1 votesI don't WANT to put down people.
OkayTrash1 votesI guess I don't have any right to put down people out of rage. AS I see it.. they caused my rage so i get mad at them lol.
Godhri2 votesYou have the right to do anything you want to do. This isn't about rights. It's about how we justify our actions and how we are held responsible for them by others (in this case, Riot).
Godhri1 votesI'm not saying you want to. I'm saying that based on the way you wrote your words, part of enjoying the game is to be able to put people down without consequence.
OkayTrash1 votesNo I would like to see IF i was to get reported for verbal abuse maybe look at what the other player was doing? Maybe i could've worded things better. Because If your going to troll me I WILL be an asshole.
Godhri1 votesI'm not sure it would be effective use of resources to investigate every report thoroughly. Hence is why they only really observe what the report is for and if the alleged offense was committed. If you want them to do the same for the troll, you could report the troll.
Drakzul2 votesRiot wants to promote all this but has an option for you to mute, and turn off language filter. Seems like they are okay with people using "vulgar" language. I mean I'm probably the minority but it honestly pisses me off when you waste my time. I work full time I would enjoy to play a game without a 12yr that gets butt hurt. If I've insulted someone they generally deserve it one way or another. I just don't see anyway of fixing the problem of idiots? I always think maybe if I guilt trip them into doing something they may change.
Riot has stated multiple times they couldnt give less of a fuck about mature language. They care if you use it to insult others.
Matthias91193 votesI work full time I would enjoy to play a game without a 12yr that gets butt hurt.
I work full time and I would enjoy playing a game without alleged "adults" who can't control their behavior.
OkayTrash1 votesI control myself very well. However in certain situations as I'm sure all of us have been in we lose it. I'm just trying to say if you troll or feed expect someone to get mad. If they do get mad and verbally abuse someone i don't see how that would be ban worthy if the other player is baiting. Because i know trolls and feeders almost never get punished.
Sarutobi3 votesi would say if you get that upset from a simple game that you need to harass other players over a game you either need to take off of the game, or find something else to do with your time!
OkayTrash1 votesOnce again missing my point but okay.