I can't imagine the parasites in cat feces being any worse for the environment than other animals. Also, I would have thought the waste from the sewer systems, etc. gets processed and treated.
The waste from the cat genie being flushed can't be worse than the dirty litter from conventional cat boxes being dumped in landfills, or wherever else. The rainwater runnoff from that would carry bacteria too.
Check out this CDC page on Toxoplasmosis: http://www.cdc.gov/NCIDOD/dpd/parasites/toxoplasmosis/factsht_toxoplasmosis.htm
According to the above, humans as well as infected raw meat could contribute as much as the cats.
I may be wrong in this, but this is just what I think.