1 - It's not stupid, it's actually effective.
- Yelling (shouting, cursing, etc; vocally expelling) helps to burn out anger and pain, so it can work as a form of stress-relief. (seriously, go look up Mythbusters - No Pain, No Gain, they've tested it.)
- Watching funny things (or endearing things, whatever makes you happy) lightens your mood and makes you less negative, which, again, relieves stress. It can also help you distract yourself from the negative experience of the game, which further helps.
- Physical distractions are also equally therapeutic (throwing a ball at a wall, squeezing a stress ball, screwing around with a fidget spinner, etc.), and so, lo and behold, relieve stress.
Typing, however, does not relieve stress, as all you're doing is channeling that negativity into a chat pane, not actually doing much if anything to alleviate it. Which, also, helps even less if the stressor is still there.
2 - Some people don't like when others complain about stuff, and believe it or not, emotions, even through text, where there is no emotional inflection, spread like a plague. When you type out all your frustrations with X champion or whatever, you're liable to spread that negative attitude to your teammates.
And when your teammates catch your negativity, they play worse, which, who would've guessed? Creates a negative experience.
Nobody's expecting you to laugh when you get frustrated; everyone deals with frustration, we understand it, but we don't want any Debbie-Downers spreading their negativity and impacting our performance.
If you want to complain, go find somebody that you know will listen; you can burn out to them, but do not expect strangers to want to listen to your ineffective venting.
