IMHO, a tester is a person who strongly believes that bug can't help being. And if there is a bug there is a way to find it. Or there are several ways, so there are different options - either methods will be expensive or time-consuming and requiring efforts.
The aim of testing is to reduce the risks occuring during software development, ranging from not working Software to the issues with deployment and installation.
It means to find ALL bugs is very difficult and often economically unprofitable. But to bring them to an acceptable level is possible and necessary.
Is it possible not to test? YES ... If it is going to be your last release of the app which no one will use :)
But if we want to develop our product in the future we must plan the testing. Planning does not mean description of each atomic step. By high level planning we describe how and what we want to reach as a result.
There are lots of opponents of planning who see it as a rigid framework that limits creative people in programming and testing realization. But I consider such people as the man with the tumor, who, instead of going to the doctor and start working on the treatment plan, thinks that everything will resolve by itself ... IT WON'T! Besides, customers want to know the exact release date of the ordered software - that is (horror of horrors!) required for planning (planning again? Are you kidding?) the customer's business.