Is mac sierra protecting me from erasing my hard drive and my sd card
Only the super user can normally perform this action, except when using the diskutil command, which incorrectly allows it. The full command you should use would be sudo newfs_msdos -F 16 /dev/disk2s1. You will have to enter your password to continue. Although, I would suggest using FAT32, because FAT16 is likely inappropriate for your SD card assuming you bought it sometime in the past decade. An even better option would be exFAT, assuming all the devices you'll be using this SD card in support it.