You're right that you absolutely can run into problems when dealing with industrial level. One of the major ones when dealing with trash is contamination. But these are not insurmountable problems. The primary difficulty is education.
We also need to get more recycling plants built more places, even if we start using less plastic, because we still have so much out there.
Easy in the backyard, very complex at a industrial scales that require profitability, stability, and air pollution control.
If you build a gasifier correctly, you shouldn't have any problems with pollution, as it should be collected. Of course, if you don't build it correctly you can get carbon monoxide poisoning.
Well, yes, of course. But such a small statement contains a huge amount of capital expenditure and engineering expertise.