Is there a reason we fear irrational things in life? It seems strange considering fear is a defensive mechanism against things that cause harm.
There are many reasons for this fear and it has been studied by many scientists, psychologists included, but I cannot go into detail at the moment! However, here are some of them:

1 - Fear based on scarcity thinking leads people to think their chances of survival are smaller when they have nothing compared with when they have everything
2 - Fear can be rooted in negative experiences you had early on in your childhood which may still affect how you see certain situations now, such as spiders or other creatures being associated with danger 
3- Most importantly though, the human mind does not function the same way a computer would and therefore fears make us act differently than what logic tells us to do (this is more important than scarcity). 
    So let me rephrase this point because i got carried away: yes it might seem like irrational fear makes no logical sense especially from a modern standpoint where all kinds of dangers shouldnt exist anymore but keep in mind most of our emotions came about through evolution. The reasoning behind those old behaviors just doesnt work any longer without emotion attached.