Determinism and ethics

I might have been mislead, but it seems that when we discussed the differences between determinism and free will, we seemed to come out primarily in favor of determinism. We also discussed how determinism impacts ethical theory by completely negating any kind of morality. Morality implies choice, and determinism does not. So how exactly can we discuss morality under any circumstances if we can not get by this first problem? It seems to me that the construction of morality is just that if we can't get past determinism: A construction. If there is no such thing as morality, then it must be an illusion that we construct ourselves. I really do not like this conclusion, but unless I figure something else out, I must stay behind it.

Does 'Is' influence 'ought?'

So, I have been thinking about our class conversations, and I believe that our views on what 'is' can at least influence us to what 'ought' to be. My reasoning behind it is till a bit fuzzy, but I can at least provide a hazy example of how we use what is to influence our ethical decisions and beliefs.
For example, ancient civilizations used to sacrifice humans to the gods in order to live a good life, and to keep the gods appeased and content. Back then, it was a 'fact' that the gods demanded these sacrifices and that they existed. Now, because we know these deities do not exist, we ought not to do that, for it is pointless to do so.
In addition, we know that other people feel pain, and that influences how we treat others, our knowledge of death influences our moral actions and decisions, our belief on whether god exists influences our moral actions as well. There must be some relationship, but I fail to see the exact relationship.