Sharing accounts is a no-no, but smurfing and roflstomping new players is A-OK.
@Riot, I'd like context on why you choose to allow highly skilled players to almost 1v5 new players, yet you don't allow the sharing of accounts.
If you think players should be allowed to create another account, add sort of a "prestige" option once you reach level 30, whereas you can create another account that's level 1 without retaining any of your champs / skins / runes, and allowing you to switch between them in game.