One reason this can happen is because of phobias. Another reason people are scared of these things is that some fears and phobias can be hereditary. Some people could have a fear of that specific thing from their childhood. It could also just be instinct to stay away form something you think looks scary, or dangerous.
What the parents did was horrible. Just so messed up It was really sad. I hate that that happen to gabriel fernandez but there are evil people out there that take innocent lives sadly.