Incinerating garbage, "thermal treatment", and "energy-from-waste" (or burning garbage to make energy), is bad for the environment and our health, no matter what you call it.
Burning waste creates pollution. The combustion process releases toxins in the solid waste, and actually creates new toxins. "Modern"incinerators may have fewer emissions than older incinerators, but they still create and release toxic pollution.
Burning waste wastes resources. Once waste has been burnt, there is no future opportunity to recover recyclable or reusable materials. New recycling techniques are emerging all the time. Only a few years ago it was considered too expensive to recycle styrofoam and plastic bags, now these are accepted in Toronto's Blue Boxes.
Burning removes the incentive to reduce and recycle. Incinerators are costly to build, and operators need guarantees about the volume of waste they’ll get to cover their costs. This creates a dis-incentive to reduce waste and to recycle new materials, because there is always a need to find more waste to "feed" the incinerator.
Finally, energy-from-waste is a dirty, non-renewable and toxic energy source. We have the technology to reduce our energy use and to choose clean and green energy sources like solar, wind and hydro.