This is a common objection among internet Atheists. It seems like they believe this one challenge to Christians really backs them into a corner. Does God just not care about amputees? If God existed He would heal amputees, or even one amputee. None are healed, therefore God most likely doesn’t exist. If only God would heal an amputee (in a scientific lab, on video, in the presence of many scientists, and repeated on command) then I would believe. You know what? I doubt it and here’s why.
Suppose God did heal an amputee. Let’s say you, the Atheist, was convinced it happened and became a believer in God. What would happen to that belief if the amputee (possibly yourself or a loved one) fell victim to another tragedy? What if you were in a liquor store while it was robbed and were shot by the assailant and became paralyzed from the waist or neck down? Would your belief waiver? I bet it would, even after you saw that God healed an amputee.
Here’s the thing, if your belief were based solely on what God does for you, it’s pretty likely you’ll give it up when it seems like He stops giving, like some religious gold-digger. Remember the Jews of the Old Testament were reported to be direct witnesses to the miracles of God and yet some still wouldn’t bend the knee. The same happened in Jesus’ time. The same would happen in ours.
Fortunately, you the Atheist, feel like you can make that boast firmly believing you’ll never be faced with the healing of an amputee. That’s OK, I’ve made vacant promises knowing I wouldn’t have to pony up too. I promised my oldest daughter I’d give her $1000 if there were no school dances this year. She is convinced there wont be, I already know there are. It’s easy to offer a concession on conditions you think will never obtain, but there’s no nobility (or integrity) in that. Just keep that in mind.