TBH, I'm not really sure of the motivations or efficacy of the coles and woolworths move away from plastic bags. I'm just concerned with the use of plastics in general and why its necessary to justify their use at a personal level. As I said, I moved away from single use bags ages ago, so the move by the large supermarkets to switch now is kind of irrelevant to me, so I'm not defending them at all - just questioning the resistance from consumers.
My concerns are with depletion of resources (and biodiversity) through consumption and pollution. Plastics do a good job of this in both regards. Plastics themselves aren't the culprit though - like has been said, if used properly they make a lot of sense and provide us with manufacturing options we simply can't get from other materials. However, there are simply too many irresponsible humans and companies that are content with shirking responsibility for their use and they do end up in natural systems. The more single use plastics we take out of the equation, the less there are for idiots to release into the environment, and the less ending up in landfill - which is not as much "out of sight, out of mind" as we like to think.