PET burns very clean with enough air. I use it as a fire starter for outdoor fires.

A fireplace is a smoky thing, without enough air (even the wood makes a lot of smoke). An incinerator makes sure to supply enough air.

Industrial waste incineration is not at all the same thing as burning trash in a backyard fire.

I recall throwing some plastic bottlecaps in fireplaces during my youth. IIRC, they'd get melty, then the puddle would ignite and burn very hot, until it was spent, and that would be about it. Might have smelled funny, but I can't remember that far back; was less sooty than the wood at least. Of course, water bottle caps aren't likely to have food waste or much of anything else other than the plastic, maybe a smidge of water and some fingeroils from handling. I also didn't have a gas spectrometer or anything, and the fireplace wasn't an industrial furnace with process controls and what not.

On the topic of food waste, my time in the kitchen says most foods will burn just fine. Although, they often leave residues that I could see being problematic when they build up.

As with everything, you'd need specifics to determine the right tradeoffs. It would seem to me there's potential in reducing the transport distance and land use of solid waste, and also reducing extraction, transport, and burning of some fossil fuels, if a burn the trash for electricity program works. But specifics matter, of course.