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@Torsten: actually, I changed my mind. That's not cheating. You can certainly get nice quasi-Lie algebras by tensoring graded Lie algebras with $\mathbb Z/2\mathbb Z$. But it would be nice to have examples over $\mathbb Z$ which contain something besides $2$-torsion.
I don't see what goes wrong if you define a "better" version of the Lie operad by taking the standard Lie operad over the integers, and modding out by symmetric trees of the form [x,x], as Gindi seems to be suggesting. Incidentally, the skew-symmetry axiom defines what's called a quasi-Lie algebra, so the standard Lie operad should really be called the quasi-Lie operad.