I think Locke knew that the rest of the Losties would disapprove, so he taught him in secret. Honestly, so far I really cannot find any malice in Locke. In each circumstance, I think he truly believes he is doing what is best for everyone, even when it turns out he's wrong.

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"Not all who wander are lost." - J. R. R. Tolkien

"You cannot live a perfect day without doing something for someone who will never be able to repay you." - John Wooden