So, why did God let Satan do it? God IS more powerful than Satan, right??
A good example of this, is the story of Job.
I would say that by allowing Satan to do anything, is how he defeats Satan. Satan is actually thinking that he will draw people away from God, but I think that in the long run, all things point to God, even what we call bad.
The only free will we have is to choose whether it is from Him or not.
note: this is my current opinion.