Since early childhood, my husband (whose family was raising him to be a Christian) was deeply disturbed by this very metaphore: that God is the Shepherd and we are his sheep. He cites it as one of the earliest times he can remember that he began to have doubts about the religious stuff he was being taught.
His thinking was along the lines of: what does a shepherd do with his flock?
Well, he protects them from predators (not always well – just puts in the minimum effort for maximum result), but not because he loves the sheep. Rather, he makes a living out of treating sheep as a commodity, to be fleeced, milked, traded as ‘stuff’ and eaten. This, even as a child, he thought was very, very ugly….
Thunderf00t expresses similar thoughts on the “The Lord is my Shepherd’ metaphore: