Plastic grocery bags vs. the prospect of disposable and biodegradable hemp bags.
The "not a petroleum product" and "biodegradable" elements seem to be the only points that matter to people in this debate. But there are far more nuances to be considered than simply plastic is bad and biodegradable natural fibres is good. In some ways, it is the same analysis that should be applied to electric vehicles, yes, they are "cleaner" once running, but are they overall cleaner when considering their footprint in manufacture?
For a serious environmental policy analyst, the relative amount of energy needed to produce a hemp bag vs. a plastic one matters. Especially since most bags go into landfills where they can cause no post-production environmental harm. A product being biodegradable is no trump card if its post-production environmental harm is no less than its competitors but it takes more energy to produce. (Also, how long do these hemp bags take to degrade, and what chemicals are added to them?)
Another important element is the type of land shifted into hemp production. If we shift land from producing some of our vast surplus of corn, that's a plus for the net environmental effect of hemp bags (if what I've heard about the relative environmental effects of growing hemp vs. corn are correct). But if we expand agricultural acreage we may end up destroying wildlife habitat.
Unfortunately, being environmentally friendly isn't as simple as "plastic bad, natural fibres good." Life would be easier if it was.