I understand that the arduino pins can handle up to 40 mA
If you want to drive motor both directions you need at least motor driver IC
Atmell guaranteed only 20mA in continuous use
No you are miss reading the specification
I think that atmell datasheet is clear
Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
40mA is the point at which damage starts to be done.
Outputs can source more mA that they can sink-> have a look to the I/O schematic and you will understand that this is normal.
Figure 10-2 shows a functional description of one I/O-port pin,
Although each I/O port can source more than the test conditions (20 mA at VCC = 5V, 10 mA at VCC = 3V) under steady state conditions (non-transient), the following must be observed:
During 40 years in R & D I've never seen colleagues take such risks.
Have you never worked with a safety department, they do that sort of thing all the time.