I don't think anyone is advocating adding plastics to the soil.
Styrofoam is not plastic, from what I have read. Polystyrene breaks down into its basic build block which is styrene, a naturally occurring organic compound found in things like cinnamon and strawberries. Unlike strawberries, it might take 500+ years for Styrofoam to break down. Since nobody recycles or reuses Styrofoam, it just fills up the landfills as trash. Not a good thing.
Having said that, the issue was that Leon, from the YouTube channel "Gardening With Leon" was advocating using loose fill Styrofoam balls as a potting mix amendment to replace the more expensive alternatives of perlite and vermiculite. I became interested in maybe using Styrofoam in my homemade potting mix because I can no longer get bulk perlite and/or vermiculite locally. My local Menards stopped selling it in the big 3 and 4 cubic foot bags for $20.00. Now you have to buy it in small 8 quart bags in the garden center at 3 to 4X the cost, or about $60.00 for the equivalent to the large bulk bags.
However, I found out that I can order the loose fill Styrofoam balls for the potting mix for less than $1.50 per cubic foot, or about $4.50 equivalent to the large bulk bags. That is a lot less expensive. Of course, Styrofoam only provides aeration to the potting mix and has no ability to retain water. I guess that makes if more like perlite, because the advantage to vermiculite is that it retains water.
For the past number of years, I have been making my own potting mix with homemade compost. My potting mix is 1/3 compost, 1/3 perlite or vermiculite, 1/3 peat moss or coconut coir. This year, I will need something to replace the vermiculite which is no longer sold at our local stores at the bulk bag rate.
Does anyone know why bulk vermiculite has been discontinued? I have asked the stores, but nobody has a clue why it is no longer shipping.