Is the opposite of dangerous. Being informed helps people make better decisions, and on a macro scale it helps society progress by not basing the collecting decisions on erroneous or untruths ideologies. The example you gave is theoretically possible and it may have happened once a century but, the reality is that people that does not believe the religious belief of free-will, do not behave like that.

You gave an argument against free will based on Determinism, but there are other good and even better arguments IMO. Like the science-centrist arguments of Neuroscience , Psychological and the Evolutionary Arguments. Then there are the philosophical Arguments from Divine Predestination or Fate. There are still more but the fun is on the discovery.