Hey Ronni,
Yes, the erythritol or xylitol is necessary to have them be "no carb" sweetened. If you are on the low carb diet, or paleo. But if you don't care about carbs, sweeten them with whatever tastes good to you! But the point of the recipe is keeping them in a low-carb high-fat state. You can probably order the erythritol or xylitol on line. That's how I get mine. ;-D These sweeteners are natural sugar alcohols that actually do contain glucose, but it's in a format that the body doesn't recognize, and gut bacteria don't consume, so most of it is excreted in the urine (90% of it), the rest is processed in the liver. I have read that these two sugar alcohols are derived from corn. You can read a little about it here: http://www.livestrong.com/article/556918-the-disadvantages-of-erythritol/
happy eating!!