Not only reduce outdoor and feral cats our wildlife dramatically but outdoor cats are also the main vector for toxoplasmosis.
A checked by a vet and contained cat is tge safest cat for their keeper, all other land creatures as for the marine life.
Please listen to this video of a person how it is to live with the animal disease toxoplasmosis. .. http://halo.org.nz/living-toxoplasmosis/
Read more here about toxoplasmosis: http://cmr.asm.org/content/25/2/264.full
In marine life:
Domestic cats and wild felids are the only known definitive hosts capable of shedding T. gondiioocysts in their faeces.