Testing needs more creativity, Logical thinking, Breaking attitude and different point of views. Then only a tester can break 100 developers developed code and catch possible missing of them. So no doubt its 100% manual resource involved work.
So then why we need to automate an application?
Automation is an assistant of a Manual tester to give extra time for think about new sequences rather checking the routine of already developed sequences by them working or not. So never an automation tool can replace a manual tester until the product is dead (no further development ).