Your first statement is incorrect.
"Your ethics allow you to murder innocent individuals too, including babies, you'd just be doing it in a different way. In fact I believe everyone has a line like that somewhere, a set of conditions that make killing tolerable."
Not curing cancer is not the same as killing innocent people, because I have nothing to do with cancer and no responsibility to cure it. There is no set of conditions that makes murder ethical, because murder is inherently unethical. Saying murder is okay if you think it's justified is a dangerous standard to have. What's a just cause? It's whatever you believe it to be. I might think murdering you for a toaster would be just, and since you agree that murder is okay if it's for a just cause, you should theoretically be okay with me murdering you for my just cause which is to get a toaster. It's ridiculous and dangerous to start allowing murder to be okay.
In regards to the sandwich scenario, this isn't a sacrifice; someone is coming after you to MURDER you. You don't actually get a say, because someone else has decided that your death benefits many people and is thus a just cause for murder. I'll say again, MURDER IS NOT ETHICAL BECAUSE IT IS INHERENTLY UNETHICAL. Do you believe that other people have the right to take your life? Do you believe that they have the right to decide your fate for you? If you don't think other people have this right, then what gives you these rights over other people?
There is a right answer, a moral answer, to this scenario. Hint: it's the one that doesn't require the murder of an innocent person. There is something truly wrong if you believe murder is ever okay. If you believe that an innocent person's life can and should be taken from them for something they have no part in and no say in, then your arguing for something entirely evil. I'm sure your motivations are pure, but your beliefs and the actions you'd apply to this situation are evil.