[Gardener]

But he had another opportunity near the gate when he revealed he was the HBP and still didn't kill or kidnap Harry.

[Ronin]

But when another Death Eater hit Harry from behind Snapes warned him off by shouting "No! Have you forgotten our orders? Potter belongs to the Dark Lord! We are to leave him!"

So by my reckoning the mere fact that Snapes didn't kill or kidnap Harry is meaningless.

Jury is still out on who's side Snapes is on.

[kevkrom]

But he had another opportunity near the gate when he revealed he was the HBP and still didn't kill or kidnap Harry.

Not only that, but looking beyond the sneers and taunts, Snape was still trying to teach Harry on his way out -- reminding him that he needs to learn to close his mind and use non-verbal spells.