There are several important traits that distinguish a specialist - namely, the ability to properly diagnose and treat any sort of cases as well as deal with complications and be able to inform the patients of what is a reasonable/ realistic outcomes. Allowing anyone to promote him/herself as a specialist would put  the general population at risk for treatment that is simply not presented or done as throughly or accurately as a specialist can. Sure some cases would turn out ok, but there will be many that won't and only a specialist be able to determine why and how to correct the unexpected outcomes. Specialties are there for a reason and it's to provide the highest possible care for the general public. This is our job as doctors and we need to protect that privilige.