I would also like to add my 2-cents about outdoor cats.Since most of us here are not lucky enough to live on a farm,indoor cats are are almost always the only choice,I 've seen many and they are happy well adjusted cats.
Life-expectansy for"out-door cats"is about 5yrs,while indoor cats can live 20+happy years.
My own 3 cats,do go outside,but only in my backyard with me and are always more than happy to go back inside and lucky for me,in -15C they only stick there paws outside and that's it and in extreme heat and humidity,they so prefer a cool house.
The city streets is no place for a cat,but that should not keep cat-lovers from having cats and indoors will have to be the only alternative other than being scraped off the street.Luckily I have big fenced backyard and my cats can climb trees,eat grass and whatever else they want to do,under my watchful eyes.
So,there are pros and cons to every situation