How is LP loss determined?

Lately, ranked for me has been a huge downfall when it comes to getting people who quit (afk, flame, leave the game, intentionally feed etc.) after dying once. I cant even get a positive score without losing with 23 LP being deducted for a toxic team. My main question is how is LP loss determined and if it is based on win/loss, why was I losing a large amount compared to gaining LP when having a positive win/loss in a previous date? If MMR is a factor, why do we have MMR to determine who we play with based on our rank? Why not have it where plats play with plats, or gold play with golds, instead of getting random people from random divisions that are for some reason extremely toxic? In my opinion, I don't find it fair if my opposing team has more higher ranked platinums compared to my team who for some reason has 2 golds and the lowest is G3, (being plat at the time). Champion masteries don't honestly mean anything if youre just going to lose 23 LP after going 20/3/8 or something like that. As arrogant as it may sound, I don't find it fair being placed on a team whom I am better than and placed against a team who is better than myself and the team I'm currently on. Playing ranked since season 2, nothing has been as stressful as this year. Before, you came out of a game think you actually did something and your team actually tried winning. Now, a person dies and someone on the team just decides its game over, brings the morale down and the blame game begins to happen.

I would love to get some positive feedback or discussion on whatever I have mentioned. I would also appreciate a Rioter response to shed some light on the subject. Because this is a huge problem not just for me, but for most likely a lot of people. Thank you.