Wrong! Word spreads quickly to job candidates. And job candidates judge prospective employers by everything they experience about a company, from job description to interview to employment to departure. And they hear a lot about those things from rumors originating from current employees.
When applicants hear that resigning from the company means they'll never be welcome back -- whether as a visitor to the company or as a boomerang employee -- they lose interest in ever starting a job. Perhaps most importantly, it also makes them less likely to refer future candidates to the company.
Remember the lunch you bought your new hire when he/she started the job? Buy it again when he/she resigns to work elsewhere. In the long run, the goodwill will pay off.