I think you're getting a lot of unfair pushback on this, when you're making some excellent points. Just to clarify, I think you're making these points:

- Existing air pollution causes a ton of harm.

- Realistically, the optimal amount of air pollution is probably not zero.

- Logically, we should treat the cost/benefit of adding this "new" air pollution the same as the cost/benefit of removing existing air pollution.

- As an absolute number, the harm caused by this facility is very large, but as a percentage it is tiny.

People seem to be interpreting your conclusion as, "therefore it's completely fine to build this facility because only percentages matter, not absolute numbers." But I think your conclusion is more like, "our society has a complex relationship with air pollution and our existing choices reveal that we are willing to accept some air pollution sometimes, so you have to do a cost/benefit analysis, not just look at costs."