I guess if they can believe random chemicals came together and created a encapsulated living being with the ability to find/intake/metabolize compounds for energy, sense its surroundings, move about in its surroundings, and reproduce itself precisely - if they can believe that, they can believe Stonehenge is the handiwork of a huge chunk of ice.
That isn't what the claim is -- the claim is, humans didn't quarry stones in Wales and drag them or raft them to the Salisbury Plain, instead, the stones were glacial erratics, gathered from the vicinity, and shaped as needed.