Me nick and O Pesha spent most of the night leveling down and had a blast.
We would beat the hell out of people and leave the game when we got to 49 kills...Muwahahahaha
A few games we tried to kill our selves and one game we ended at - 135 kills.
People were pissed

If you leave the game at 49 wins (presuming the win is at 50), it's pretty much a slap in the face to the other team. And really no different than trash talk (which is really annoying and poor gamer etiquette, imo).
If I were the other team, I wouldn't blame them for getting pissed. And even though you give them the win, it still not fun because it's not earned.
I play online becaus I enjoy the competition. Whether I get beaten the hell out of (which is often) or not, I enjoy learning the game and it's strategy. And we learn by playing against people with better skill then our own.
No offense, but I just don't see any benefit to it no matter how much justification is given that they "got the win".