I need to validate an input string from the user to ensure it's a 32 character hex (I'm validating it's a NAA format 6 WWN) and regex is just the easy, fast and

I need to validate an input string from the user to ensure it's a 32 character hex (I'm validating it's a NAA format 6 WWN) and regex is just the easy, fast and efficient to do this. It's not a complicated regex and is quite readable to anyone with basic regex knowledge, why is this wrong?