Well if you eat meat, I feel it would be somewhat inconsistent to consider dissection immoral. I'm not going to assume you do, but I think that education has as much power to do good for the world as food does. Also, hands-on education is probably much more valuable than a computer model.
When I think about whether it's right or wrong to kill animals, I like to go back to what makes death sad, because I think that is the crux of the issue. In my mind, this is how I break it down. Death is sad because:
1. The loss felt by those around you
2. The loss of the potential future of the dead
3. The suffering or fear felt by the dying
I'm open to other reasons, which may or may not change my argument, but to me that breaks it down. For instance, the death of an elderly person is generally accepted as less tragic than that of a young person because of reason #2. A quiet death in one's sleep is less tragic than say, a fatal car accident, because of #3. There really isn't any human death I can think of that doesn't hurt because of #1, though.
If we apply this to an animal's death, though, I think many of these don't apply. Again, #1 arguably applies to most livestock animals (probably not to frogs and non-social animals, though), although it could be argued that they probably don't feel the kind of stress that humans in that situation would. I imagine they miss their companions but, lacking critical thinking skills, haven't figured out that they were killed. This is probably the worst aspect of killing animals. Personally I don't think #2 ought to apply to animals. Call it cold-hearted or selfish, but the frog was going to eat flies the rest of its life, the cow was going to moo and eat grass. They don't have hopes, dreams, or long-term goals. As far as I'm concerned, #2 only applies to sentient life. Again, I'll qualify that I understand that what I'm saying isn't conclusive proof, but this is how I view it. #3 is one that may or may not apply to animals. Obviously, every possible effort should be made to make the death as painless as possible. There is really no way to understand whether an animal product you are using violates this without finding out where and how the animal was killed.
So I hope that at least helps you think about this issue. I know I've done a lot of thinking about it after having a vegan roommate : P.