Edit: to be clear, I'm asking this because I'm actually curious about the answer. A quick Google search doesn't find anything particularly convincing.
If you burn it for heat and electricity, this is actually an excellent use for it. As long as your region has oil- or coal-powered plants, burning plastic waste means that you got more use out of the oil than if you had burned it directly.
You are absolutely correct in that recycling is an unquestioned good, everyone "knows" you should recycle, but noone thinks about what it means and what actually happens with the stuff that gets recycled, or how it is recycled, or if it makes economic or environmental sense to recycle a material.
In Sweden, which doesn't really have landfills, and where recycling is also elevated to some kind of saintly status, there was an article published by some environmental agency a couple of decades ago which challenged this. They basically got labeled heretics, but the points they made were actually good:
1) Aluminium should absolutely be recycled, the energy costs of converting bauxite into aluminium are astronomical, compared to recycling used aluminium containers.
2) Glass should be recycled for the same reasons, it's cheaper and easier to do than to make new ones.
3) Newspaper, cardboard, and similar low-plastic paper products should be recycled, you can easily make new newspaper or cardboard out of it, saves you some trees.
4) The rest - fuck it - burn it all. Recycling plastic is hard, you can't turn it into high-value plastic products such as clear plastic packaging, you can only make low-value plastic products, and then you might as well burn it, and offset your oil-powered plants.
Sure but that could still mean that it makes sense to sort it? Can you burn plastic trash more efficiently than mixed burnable material I wonder..?
Also, one big reason that we have less landfills (I'm pretty sure I've heard that we have at least some for some particular purposes) - is that we do a lot of incineration. We even import from neighbour countries.
Sure, probably, but now you need a trash incineration plant and a plastic trash incineration plant...
Screw it. Burn it all. Modern incineration plants are very good at their job.
The problem seems to be with many of the other things that are allegedly recyclable. Just because someone somewhere can recycle it doesn't mean your local recycling facility can do anything with it.
I live in Hawaii, and I usually buy local eggs. They come in a polystyrene container, and polystyrene is something that shouldn't end up in landfills. So the company graciously offers to recycle the container for me, the only thing I have to do is mail it to Washington State. From Hawaii.
(Thankfully, Hawaii incinerates most trash, so that goes straight in the trash!)
It would be interesting to know if the environmental impact of the plastic containers for the local eggs offset the environmental impact of transporting mainland eggs to Hawaii.
Hawaii has a high percentage of oil-powered electricity, and it burns all trash, so me throwing the plastic container in the trash should offset some oil, which drastically reduces the impact of the plastic container per se. So the polystyrene containers might be the better option.
Figuring out the actual best environmental option is really really hard. And the exercise above is just for god damn egg cartons.
Then again, there's plenty of low-hanging fruit to solve before my choice of eggs start to count. If you live in a place that has landfills, that should be the number one priority to fix. Landfills are terrible, burn the trash instead, it allows you to recover a lot of energy.
My beef is that (at least the general US population) isn't aware of what the resources required to produce packaging vs. the packaged item are. Probably the plastic packing on that 1/2 pound of bacon has a small carbon footprint compared to the meat inside, but I can only guess.