I debated running my new deck with a 2 ohm load, but instead I decided to wire each side's front in series with the rear to create a 4 ohm load and just use 2 channels of the deck for the time being, until an eventual speaker upgrade. I put my deck in today and I'm well pleased with the sound, it's even bassy at low volume levels.
Concerning speaker power draw, this is going to be a function of the ohm load and the voltage they are getting. Volts (based on volume setting) divided by the 2 ohm load, equals current, and then that current multiplied by the volts equals wattage. It doesn't matter if it's a factory speaker rated for 3 watts only, or a pair of $150, 2 ohm Infinity Kappa's. 2 ohms is 2 ohms. The speakers will draw what they draw based on the voltage in and whatever ohm load they are.
The deck is maybe capable of putting out more than the factory speakers could take, but basically, with half the impedance that the deck should normally see, there is suddenly a potential for twice the current flow. So now there could be a situation where the deck puts out more power than its even supposed to (same voltage into half the ohms, twice the current, therefore twice the power), and then damage occurs. On a 2 ohm load you will reach max output of the deck long before the volume cranking ability is tapped out. The speakers may start sounding crappy long before that too, but there is still the chance that some people would turn the volume up beyond where they should (happens all the time), and not know where to stop, and with half the ohm load that makes it way worse than if it was a 4 ohm load.