Are plastic bags and containers bad for the environment?

In short, yes.

Surprisingly, though, that has not always been the consensus, and in some cases, it is not true.

In the 1970s energy crisis, reducing the weight of materials, and increasing the shelf life of goods (which helps with optimizing transportation methods) were widely lauded as environmentally positive. In short, paper bags weigh more than plastic bags, and transportation requires fossil fuels, and of course fossil fuels impact the environment in widely documented ways.

Also, some plastics like PET have great recycling track records. So if it reduces energy consumption, increases shelf life, and can be recycled it seems like a huge environmental win.

However, plastics are very durable, and now micro-plastics are everywhere. They are in the deepest ocean trenches, accumulated in many species of animals and plants, and will be for our lifetimes. Their toxicity and negative impacts are just beginning to be understood. This has driven the removal of "single use plastics" from a lot of commerce, with further reductions called for by environmental groups worldwide.