I don't think boosting is the biggest problem, it is quite rare and in my opinion there is no malice behind it, the booster just wants to quickly get the game over with and move on. Boosting is simply selling a service for which there is a demand, I'd imagine if climbing felt more like working towards a goal as opposed to an exercise in keyboard snapping frustration boosting wouldn't be as much of a problem.
Smurfing is another story entirely however, people really only create smurfs for one reason: to beat up on less skilled players. I can't understand why Riot tolerates smurf accounts, you have players in gold or plat who decide that instead of getting better to climb higher they will just create a smurf and beat up on new players. Finally after turning dozens of new players away from league because their first foray into PvP was a grey screen simulator the smurf finally gets tired and quits league entirely.
I can't understand why Riot tolerates people beating up on rookies and driving away new players but letting a bronze player get boosted to silver is so unforgivable that Riot spends countless man hours trying to stop it.