"its just normals"

I'm trying to finish off this takes way too long to earn final avatar and I keep getting terrible teammates who are literally feeding 3rd world nations. I'm talking 2/12, 0/9, 1/10, etc. It's constant. So I pipe up with lines like:

"Play safe guys" "Don't go past line of vision" "You're going out too far XXXX" "Why did you go in the jungle without vision when they're ahead 20 kills?" "Farm under turret so we don't give them more kills" "Let them have the dragon" (2 people run in 2v5, jg isn't even there to smite steal) "support, please ward, we haven't had any wards down in a while" etc, etc

I try giving non-threatening commands, I try to ask thought provoking questions about how someone is playing, I try to instill wisdom (GP, use your Flesheater.... you've had it all match and you're at 0) etc. If someone comes back with "I'm trying to learn champ XXXX," now I'm on board with why they're playing bad and throw in tips in builds/combos if I'm familiar with the champ.

I have gotten 2 verbal abuse warnings since this event started.

I'll be honest, I probably deserved the one I just got. After asking the 0/8 ADC to leave mid lane 2 or 3 times nicely (and having lost multiple matches to people feeding) I broke down and said "Go be shitty somewhere else." Was it nice? No. Do I feel bad? No.

There's only so much niceness and cheeriness I can throw out before I get frustrated from slamming into that wall of "bad." Players who don't learn from their mistakes, players who ignore the advice of others, players who take from (& hurt) their allies, etc. These players really ruin the match for me. The few times I've voiced this while playing I get the "this is normals, go play ranked"

Apparently wanting to win & caring in normals is wrong.

I have fun when matches are relatively even and end up being close games, win or lose. That's the best match to me. I don't have fun when I have a top lane yelling "I can't believe I died" after flashing under the enemy turret without a kill.

Side note: Some of the frustration is also a direct result of really bad matchmaking. I've gotten in the habit of checking people who I can quickly tell are way better than me. I see with frustrating frequency matches where me(silver) and a team of bronze/silvers gets put up against a team of bronze, silvers and 2 plats. Sometimes it works in reverse. My question: Why are any plats playing with bronzes and silvers? how is it Silver/Bronze can makeup up 75%+ of the player base but the matchmaker can't find a match for just them? If I were the plat, I'd be mad I got shoved into a lower tier of gameplay.

tl;dr I try to be helpful and occasionally snap at people after riding waves of bad, non-communicative feeders. How do you put up with this? Should I just mute all players at the beginning of the match and pretend I'm playing by myself? That's what they seem to do.