Let's not kid ourselves. You can say it's a douche move all you want but at the end of the day nobody plays the game for their teams enjoyment, you're trying to gain LP for yourself.

I can see how it's a lose-lose situation. On one hand the team is now playing 4v5 but on the other hand the person who had a DC feels cheated and really has no incentive to reconnect back to the game. It's more Riot's fault than anything.

If someone DC's because the servers screwed up or something I wouldn't blame them if they would come back and know they won't gain any LP. It's not just their team who has to pay for it, the person who DC'd also has a sour taste in their mouth and probably doesn't even want to play for a while in the first place.

Personally I wouldn't even report the person if they had a legit DC but didn't want to come back, it's Riot who's at fault there and they shouldn't ban a person when it's their game / servers that screwed them over.