It's not completely free; it costs 4 life for every snuff out you play. With all the life lose you're playing - Dark Confidant, Snuff Out, and Wretched Anurid - you're causing yourself a lot of pain. Plus, if Dark Confidant rips a Snuff Out, that's going to hurt twice as much as Smother. Anyway, I'd much rather hold back turn two for a Tarmogoyf, kill it, and then lay Nantuko Shade and proceed to beat every Tarmogoyf that comes down.
Also Wizards printed Gaddock Teeg. That card shuts down Snuff Out. Smother can kill Teeg, Snuff Out can't.

