Apple - I can't write to my flash drive, and it is already in the MS-DOS (FAT) Format. Why?

So, here's what I did after much face-palming and cursing of Apple and their absolute disregard for their users:

From the terminal:

1. Identify your USB by NAME and IDENTIFIER:

diskutil list

Output is:

/dev/disk3 (external, physical):  
#:                       TYPE NAME                    SIZE    IDENTIFIER  
0:               FDisk_partition_scheme              *2.0 GB     disk3
1:                 DOS_FAT_32 MIXTAPE                 2.0 GB   disk3s1

In this case, NAME=MIXTAPE and the IDENTIFIER=/dev/disk3s1

2. Now unmount the USB:

sudo diskutil unmount /dev/$IDENTIFIER

Example:

sudo diskutil unmount /dev/disk3s1

Output is:

Volume MIXTAPE on disk3s1 unmounted

3. Now create the Volume directory - this appears to be the key!

sudo mkdir /Volumes/$NAME

Example:

sudo mkdir /Volumes/MIXTAPE

No output.

4. Now mount the USB to the Volume:

sudo mount -w -t msdos /dev/disk3s1 /Volumes/$NAME

Example:

sudo mount -w -t msdos /dev/disk3s1 /Volumes/MIXTAPE

No output.

5. Validate that the USB is now writeable:

touch /Volumes/$NAME/tmp.txt

Example:

touch /Volumes/MIXTAPE/tmp.txt

6. You should now be able to see that you were able to create the tmp.txt file on your USB in the Finder app or by:

ls -al /Volumes/$NAME

Example:

ls -al /Volumes/MIXTAPE

If you don't need to use this USB disk on a Windows machine, format using Mac OS Extended (Journaled). Should you need to exchange files with Windows machines, then Format as you have with MS-DOS (FAT). ExFAT should work as well.

It is not outside the bounds of possibility that the drive itself has gotten zapped somehow and is damaged, thus not operating correctly. Copy all the files from the flash drive to a folder, reformat with MS-DOS (FAT), then see what happens when you copy back. If it doesn't work, chuck it. Since flash drives are so inexpensive now, get a few more of them in larger capacities.

Lastly, (above) some flashdrives have a physical write-lock (read-only) hardware switch. If your flash drive has such a switch, perhaps it is locked? OS X does not allow the usual file & directory permission on MS-DOS (FAT) disks, so you can't try to make it read/write.

There is also a 4GB limit on a single file in MS-DOS (FAT).

This is a stab in the dark, but is your USB drive actually an SD card in a card reader? In this case, I would tend to think the hardware write lock switch is in the on position on the SD card.