Why would one want to reduce plastic usage?

A friend asked why someone would want to reduce plastic usage. It’s an interesting question. Plastics are very useful (versatile, lightweight, long-lasting, relatively low carbon footprint), but there are people who want to avoid all plastics (see My Plastic-free Life, for example). In fact, a lot of people in the zero-waste community are anti-plastic to the extent that they replace functioning plastic reusables with items made of other materials (not the best thing to do, by the way!) .

Pros of plastic:

• Doesn’t decompose in landfills, which makes plastic good for sequestering carbon. (FYI biodegradable and compostable materials are only worth using if you actually compost them. If you put them in the landfill, they will produce methane, which is a much more potent greenhouse gas than carbon dioxide. Plastic, on the other hand, sequesters carbon basically indefinitely. It is ideal for landfills.)
• “Natural” materials, such as paper and cotton, generally require more resources to produce than plastic (for example, although this apparently isn’t true for some types of synthetic fabrics, where the plastic has a small footprint, but processing is very resource-intensive), so plastic may be a better choice of material for single-use items (e.g. packaging, medical disposables).
• Durable, in some ways. Unlike glass and ceramic, plastic doesn’t usually break when dropped. This can be good for storage containers. Plastic is also resistant to many caustic chemicals.
• Plastics have amazing and varied characteristics. Transparent, yet flexible. Lightweight. Remoldable (sometimes). Cheap.
• Plastic is lightweight, making it cheaper and less resource-intensive to ship.

Cons of plastic:

• Leaches unknown and hazardous known chemicals at unknown concentrations into whatever it is containing or touching (e.g. BPA from receipts can be absorbed into your skin when you touch them), or off-gases into the air. See Plastic Free for detailed info + citations. I’m sure there are articles online as well.
• Plastic additives are largely unregulated. Despite the recent hubbub over BPA and a lot of scary research, the FDA’s stance is that current levels of BPA in food are safe (despite the fact that endocrine disruptors may have stronger effects at lower doses (source). They even have inter-generational effects. For example, one study concluded that higher blood BPA concentrations in mouse mothers was correlated with “loss of sexual dimorphism in brain structure and behavior illustrated by animal studies, findings concordant with human epidemiological studies” (source, text). I can only wonder if BPA and other hormone-mimicking plasticizers are the cause of the apparent uptick in the number of transgender people.).
• Made from a non-renewable resource (fossil fuels). Petroleum and plastic are incredibly valuable and irreplaceable resources that should be reserved for uses where they are not easily replaced (medical purposes, for example).
• Supports the petroleum industry, which has a history of “downplay[ing] the significance of climate change [using approaches] copied from tobacco lobbyists” (source) and damaging the environment through extraction.
• Difficult to reuse. For example, many plastics are porous and can’t be properly sanitized for reuse. Others leach additives faster as they degrade.
• Can break down over time and via exposure to UV, causing brittleness, flaking, and leaching. Unfortunately, the tiny bits of plastic will still probably not degrade for several hundred years.
• Difficult to repair (although this is definitely not unique to plastic).
• Difficult to recycle. Only plastics 1 and 2 are commonly and easily recycled. Glass and metal, on the other hand, can be recycled indefinitely. Paper can generally by recycled 7 times until the fibers are too short and weak to be useful. (However, recycling in the US is not stellar for any material, largely because people want single-stream recycling for convenience. Unfortunately, this causes contamination due to materials being difficult to properly separate, so companies don’t want to use the recycled materials.)
• Not biodegradable. Stick around a long time (100-1 million years, estimates vary and depend on type).
• Cheap. Encourages thoughtless consumerism, fast fashion, unnecessary disposables, etc.
• Have a propensity to become litter. Plastic in general is lightweight and easily blows out of trash bins. Film plastics are particularly aerodynamic.
• Synthetic textiles are flammable. They also melt and release more-toxic-than-usual smoke when on fire, making them poor choices for high-heat uses (cooking and welding come to mind).

These problems can be largely ameliorated by refusing single-use plastics and by regulating plastics additives. Durable plastic goods are exempt from many of these issues.

And here’s a well-written post on reducing your carbon footprint. In summary: eat less meat (especially beef), insulate your home, and buy less stuff.