Question

explain why friction is called necessary evil

Answer 1

because friction helps us in many ways like walking we need friction, writing and almost doing every work.

Answer 2

This is a very relevant theoretical question. Friction is responsible for opposing the motion of the body and without it the body would not stop because the body will not lose it's kinetic energy. Friction is not only present in rough surfaces but also in air in water and any other matter.
It is simply necessary because obviously without it walking ,driving and flying would be very difficult.
It maintains the grip on the ground. 
But Why is it called evil?
It is simply because it is very troubling when it's magnitude is large. Moving sometimes require excessive energy.
For example on deserts and snowy regions where friction is very large.
These were my views to your question.
Hope it helps.