Hullbreaker and Sanguine Blade can coexist !!!
They are two different items, for different classes, with different stats! 
There is no point in taking one off.
You can make them "Unique Passive" or, like guinsoo and infinity, you can't buy both!
A lot of players like to build it and are having fun with some builds with it! 
Do not exist only high elo and competitive, think also of those people who play your game for the only purpose of having fun.

There aren't many lethality items and by doing so they will be even fewer, plus there is no other item with similar stats: lethality + atk speed + lifesteal.
It is unique! 
Yes, it will not be the most used item of all, but why take it off if it doesn't create problems in high elo / competitive since it is not used?
We might as well leave it for creative gamers who enjoy theorycrafting!
Theorycrafting is fun. Why remove the fun from the game?

You can add an item without deleting another! 
Save the sanguine blade!
#savesanguineblade
#riotpls
#donotremovesanguineblade