If you aren’t implementing a prototype for some quick demo in some 8 hours, 3 days, etc. to archive it in a folder like the “trash” right after that, then you will have to think about the quality assurance, finding bugs, etc. Somebody will have to do this job after all. Whether you include the automated tests in the code development process or you totally rely on the testers, the automated tests will appear in your system sooner or later (or the project will die aborning).
The worst thing is that auto tests are also the code, i.e. all problems relating to the code development (the design, bugs, usability, performance, etc.) exist in tests. When you automate the testing, you actually implement the new functionality in your system. Thus, you should develop tests as any other features.