My understanding is that incinerators don't just release the output. The exhaust is pumped back into the system and dealt with somehow. The extent to which the release is "dealt with" is the tricky part.
I'm going to guess that large amounts of CO2 is a byproduct and is vented.
CO2 is bad but not toxic at all. It's inert. The toxic ones are toxic because they still have some energy left and the earlier you pull out that energy the better. Preferably in a plant that puts that energy to some form of use.