And it doesn't breakdown into billions of micro particles that stay in the environment. (Though lots of micro plastics come from apparel rather than consumer electronics)
If you do a full lifecycle analysis on the part plastic usually wins. Even if you recycle the metal, you can burn the plastic (which is the environmentally best way to handle it) and get back virtually all the energy embodied in it.
Using a metal part, when plastic will do, just costs extra energy.
Obviously some things need to be metal for strength, I'm talking about when that's not necessary.
Read the rest of this thread. Burning plastic for energy reduces the need for oil from the ground. It's by far the best way to handle plastic.
It removes waste, it's emits less CO2 than pull extra oil from the ground, and it's cheap. You don't get a triple win like this very often when it comes to the environment.
His point might be that the carbon in the plastic will some day be released to the atmosphere, either through decay, combustion, or even digestion. Might as well burn it now and recover some energy in the form of heat from it.