I don't agree with the fears but they are not at all uncommon. I was briefly a member of an indoor range that would terminate memberships INSTANTLY if you were caught using ANY type of target resembling a human form. Didn't matter if it was a miniature silhouette or Bin Ladens face. It was Insta-Ban.
I see no particular advantage to using silhouette targets for the vast majority of shooters. A similar sized piece if cardboard would be no less useful.
On the other hand, I also see no reason why someone shouldn't use them if they want to.