Most people on the forums is either complaining about their teammates causing negative experience, or doesn't understand why he got banned after flaming someone having a bad game.
But I hardly ever see any positive posts, so here I go:
The community isn't straight up toxic. There are many friendly and fun people playing the game. But as I can see, people tend to focus more on the negative things, and ignore the positive ones. That pretty much only depends on your attitude.
I (especially as a Sona main) get flamed a lot for my main champion, like I remember games where the enemy team 4v1 dived me under bot tower, and they were like "Sona OTP btw" and "worthless egirl". And they kept saying stuff to tilt me throughout the game, and camped me a lot. So yeah, that's really negative, and happens regularly. The tilt lasts for a few games, or I just stop playing, get some rest and I'm already feeling okay again, so it's not a big deal.
On the other hand there are games where people are really nice. And from my experience this is what most people ignore. Like once when I was playing mid, my opponent was playing Lux, and suddenly she went a little back on lane, stood in one place, in the kinda way that you knew she was typing something. In my mind I clearly remember I was like "Did I do something wrong? Is she going to flame me? I wasn't even playing aggressively, didn't zone her, how did I annoy her?"
And then I just see the message in all chat Lux saying "I really love your name! ^^". And even though there had been like 5 other people complimenting my summoner name that week, this particular one was really memorable for me. I know it doesn't sound like a big deal, but for some reason it felt very wholesome, I can't explain. Maybe it's that I expected negative behaviour because that's what I mostly get in League, and then it caught me off-guard that the enemy was actually being really nice to me. And these few short, simple words brought me a way more positive and memorable moment than how much negativity the enemy team that was bullying me caused me. The negativity only lasted a few games, but thinking back to that moment when I was expecting something toxic, then got something nice still makes me smile. Most people would probably just say "thanks" without a second thought to maybe really appreciate it.
My other most memorable games are also caused by friendly teammates. Like there was a game where we started talking about totally off topic stuff, like movies, and the whole team was just so friendly and nice, I'll never forget that game. I think if players started looking for the positive things instead of the negative ones, their experience would get much much better, and there would be less need to make posts about negativity.
Another example is when I was playing ranked, my adc was playing completely awful, but I still didn't say a bad thing to him. (I never flame anyone for gameplay, I just get passive-aggressive when other people are flaming.) Then he started flaming me for no reason, blaming everything on me, blaming on me that he lost the lane, when our jungler ganked I flash ult ignited the enemy adc, the jungler also dealt some damage, then the enemy adc survived on 20 HP. My adc didn't hit the enemy once, he was just farming minions on full HP while the gank was going on. I still didn't say a bad thing, yet he still kept flaming me.
After a while his premade midlaner also started hard flaming me, to the point where I got so tilted that I tilt flashed. I don't like muting people because I don't like being talked about behind my back. So it was a very horrible experience, until our jungler started protecting me, told them to stop and said how bad the adc was and that it wasn't my fault at all. The jungler standing up for me made me happy and made the match for me a positive experience overall, even though I was flamed a lot during that match. But a good while ago I changed my mindset to be grateful for the things you have, rather than whining about things you don't have, and that really helped me, not only in League, but generally made me way happier in life.
So the moral of the story is, be positive and focus on positivity! That way the game will become less depressing to play, and you can also slightly increase your chances of winning by trying to untilt your teammates. Like when your 0/7 toplaner finally somehow manages to kill a fed enemy, say "Good job top! :D" instead of saying "It was about time you %%%%ing trash piece of human garbage".
Put yourself in his shoes. If I was doing bad in a game, I knew I was doing bad, and my teammates kept flaming me, I would just stop trying because my mood would be totally ruined and I wouldn't want to try anymore, I'd just want to be out of the game. But when they compliment me for the smallest little thing I did right, then I'd probably calm down again and I'd start focusing on the game to not disappoint the teammate who congratulated me.
Back in Season 3, I was way easier to piss off (I was 15, what do you expect), and in one of the games, the adc and the jungler were really getting on my nerves. They kept blaming me for stuff I didn't do. Like "report Sona stealing red" "report Sona taking CS" "report Sona flaming", and after a while, it started really pissing me off. Especially when I did something like accidentally stealing 1 CS, they kept spamming that I'm stealing CS, kept spamming question marks and all. Again, I was 15, and my temper wasn't as good back then, so I just said "fine, I'm not taking this anymore, I'm going afk". You need to wait 5 seconds before going afk, and I was waiting, I clicked on the confirm button, then there's that 1 frame that gets "frozen" for a few seconds when exiting. I saw that the midlaner asked me really nicely "please, ignore those idiots and play for me :(".
So then just because of that I immediately went to reconnect, they of course started the "report Sona afk" thing as soon as I got back, but the midlaner told me to not pay attention to them and started talking to me about other things, just to help me untilt. They probably would've lost 4v5, but we ended up winning the game. This is another example of how much your behaviour towards your teammates can change the game. Yes, I know that it was my young kid self, but how you threat other people still changes their mood, at least a little bit, which can be enough in some cases (again, in some cases, not often but may happen) to turn a defeat into a victory.
So next time you have something positive that happens in the game, try to appreciate it, because if you're only focusing on the people who are flaming or having a bad game, then you'll probably hate this game soon enough. Hope this post had any value for you!