How is backdooring a non-toxic element of the game? How is it fun that a team keeps getting stomped over and over in a 4v5 teamfights, only to win because the missing member has high mobility and was busy destroying the enemy base?
Take this Nidalee in my last game for example. Only 9k damage done to champions, going 2/2/3/305 in a 37 minute game (final score 21-18), yet doing 185k damage total, and last hitting 4 towers and 3 inhibitors. She didn't contribute anything to the game, other than being a chore to go and clean up for the enemy team. She would flee at any sight of a champion, and no one could hope to keep up with, let alone kill. She would never join in team fights, except she basicly won them the game.
I'm sure she was having the time of her life, but how is this in any way shape or form fun to the other players? One team is having to deal with the low of just losing a team fight and all being dead or about to be, whilst the other has their euphoria at winning a fight cut short by looking at the mangled remains of one of their lanes on the other side of the map. What counterplay is there to this other than someone sitting out and guarding the base? Or concentrating on the map in the middle of a fight, ready to drop out at a moments notice and go defend?
I have no idea how this could be fixed, as several champions are notorious for doing this (Yi, Teemo, etc), and it's part of what makes them who they are when it comes down to team fights. You can't buff towers either, as it makes them difficult to legitimately push.

Maybe I'm just overreacting. Maybe I'm just unskilled enough to know the proper 100% surefire way to deal with backdoorers. But I'm still slightly pissed off.

Win a team fight and push a lane, back dooring only works if the enemy team can equally trade you or leave you low enough after a 4v5.

I've never seen a team win from backdooring alone. I have however seen it backfire many times. If the enemy team can trade evenly 4v5 then there's a strong chance 5v5 they would win the fight decisively and be able to push into your base as a team... Imo backdooring can only hurt your team.

Not really if it's a 4v5 stand off near a turret and somelike like master yi can backdoor before you can even get there and just run off and can't be caught.

But I guess that's the fault of the team for not having wards/paying attention.

Easy, fight 4v5, win the fight, push. Rinse and repeat, you do more damage pushing as (in a 5v4 you must have at least 3 alive post-fight?) 3 than 1 Nid. Sure she's annoying as hell but as long as you keep doing that the game will end.

First, backdooring is the act of killing a turret when there are no minions around. If there are minions around, it's called split pushing. Two entirely different things, and they're met with different attitudes. Ie. split pushing is a strategy, and BD is BM.

That said, both split pushing and BDing are part of the game. Neither is BM. If they're winning fights 4v5, they would've just destroyed you 5v5, taken baron or something, then pushed harder than nidalee pushes solo.

It's a strategy. Learn to counter it.

Backdooring is strategy. This is a strategy game, not a pubstomp. If you keep losing to backdoorers, try warding more or running Teleport.

People and their unwillingness to adapt to the other team...... When will you realize that that is what this game is about? :/

I've won a game from backdooring...

I was playing Teemo. I took over their top jungle, naturally annoying the hell out of them enough that they left me alone to push. My team had fed pretty much the entire enemy team, so I just stayed top and took the objectives while my team died in team fights. Eventually, my team managed to stall them at the entrance to our base, and I forced the enemy team back when I started pressuring their nexus. We Baroned and pushed to win.

Even after all the rage, no one knows how to counter Teemo... haha

Ward the jungle since thats the main area where someone runs through in order to backdoor to your base. I've won a few matches by backdooring before,only because I wanted the match to end,last one was with Ezreal in a 3v4 match.My team and the other team were at Baron while the other team's base was destroyed already and their nexus was wide open,I decided to blink into their base and get the last hits on their nexus to end the match.

The best way to counter this issue? Do not engage the enemy team. jungle, gain CS and obtain all the buffs you can. If your backdoor champion is ganked a few times, they will learn....as long as they are engaged in the game....that they have to stick with the group. I see this, and in the past have done this WAY too much. 4v5 or even 3v5. Why? you don't stand a chance unless you are basically double leveled or have more CC than David Hassellhoff has cheesy p/u lines. Learn to control your advances, and take the opportunities that offer you the unfair advantage. Why not? The opposing team obviously is, and they continue to capitalize on it, whilst you rage so hard your pinky turns purple and your breaking an anger sweat. If you win the game from backdooring, then obviously it was the right choice. A wise man once said : "Ask any racer here. It doesn't matter if you win by an inch or a mile. Winnings winning."