They might be a huge employer but they also murder people. Even if you work in a role that supports murder and doesn't actually do it directly, I'd say that the ethical side is a concern. Certainly not something to be dismissed out of hand, even if you make the decision that you are ok with it.

I am of the opinion that a "well it's far removed from me even though that is what the organisation's main goal is" stance is doing yourself a disservice.