Well, what ever they are doing, I hope it is clearly under the creative control of JKR. I understand your point. It is similar to the scene in LOTR where Faramir takes Frodo and Co.. to Osgilith. That does not happen in the book. But in discussions with others, we think they had to do it to make several points and connections at one time. It works, but it diminishes Faramirs character in the process.
I think you are saying that the trailer scene does'nt mean Snape is being shown as protecting Harry because he's good, but for his own selfish reasons. So it would just be a device to eventually show Snape as evil.
I think this is a good point.
