"Can spirituality be misused for evil?"

Definitely. And so can anything else.

"Was human sacrifice to the fertility gods evil or simply ignorance?"

Perhaps ignorance itself is the primary thing that leads to evil.

"Do we really know if spirituality can have an effect on material issues?"

No, we don't, but it's an interesting possibility...

"Did the primitives know things that we do not?"

Sure. But they also didn't know various things that we do.

"Were they more spiritually aware then we?"

They may well have been, in some cases.

"The scientists say that humans will gradually lose the ability to walk because of our overuse of vehicular transport. Is it possible that we already lost much of our spiritual personna, through logic, reason, education, Mudcat?"

Yes, I think probably so. Everything turns out to be a compromise. ;-) You gain one thing, lose another.