The short answer is: Sort of.
It's not going to explode, if that's what you're worried about. The reason that people tell you not to do it is because it can short out your battery. It's not that it's an auto battery...it's the capacity. As you decrease the resistance (ohms) you increase the pressure on the battery (amps), the batteries that you have aren't really rated for a high drain. Once you start exceeding what they're made to do, you will severely shorten the lifespan of the battery. There's also a chance that the battery will just give up and stop working all together.
The other problem is that cartos have a tolerance of +/- 0.2ohms. So your 2.0 ohm carto could be 1.8-2.2. If you decided to go lower and get a 1.7ohm carto, you could be vaping with a 1.5ohm carto, or a 1.9ohm... Also bear in mind that the resistancce of a carto will change a bit as it gets gunked up and used.
I've used 1.7ohm cartos on my eGo 650mAh batteries, which still work. I'm not suggesting that you do so though. If you wanted to go for a lower resistance, I'd recommend picking up some sort of a mod with replaceable batteries. It'll save you in the long run, when you can buy a new 6 dollar battery instead of a whole new setup. (18650 is the preferred size, since it offers good battery life without being gigantic.)
Cheers,
-X