If you can't give a haircut then you can't give a safe haircut.
Specific example: most people expect a basic haircut for a man to trim around the ears. If I never trim around the ears then maybe I'm being safe, but you can't say I give a safe haircut because I'm not even giving a haircut as most people expect it. In particular I'm avoiding one of the most dangerous parts. You need to watch me trim around the ears in a minimally correct way to make sure I know how to do it safely.
Specific example: most people expect a basic haircut for a man to trim around the ears. If I never trim around the ears then maybe I'm being safe, but you can't say I give a safe haircut because I'm not even giving a haircut as most people expect it. In particular I'm avoiding one of the most dangerous parts. You need to watch me trim around the ears in a minimally correct way to make sure I know how to do it safely.