A simple cost/benefits analysis explains why humans keep dogs as pets: they reduce the incidence of depression by providing companionship, defend your property against intruders (human and otherwise), and have been selectively bred over thousands of years to make good companions. The positive outweighs the negative, or else we wouldn't keep them as pets. However, it does not seem that the same could be said of these Urban Foxes as the only point which can be raised in their favor is pest control, yet cities throughout the world do just fine without urban foxes of their own. I see no reason to believe that they are key to the management of the city's ecosystem (as we have other ways of dealing with pests which work just fine around the world), but if you'd like to provide research that proves otherwise since this was your claim to begin with I'd certainly reconsider my point of view.
If you're going to make the argument from a moral perspective however, there isn't really anything I can say to convince you otherwise because I don't believe that such objections are rooted in pure logic, but moreso in emotion or spirituality. I disagree with the level of moral value you're imbuing into a creature which lacks sentience, I don't think it's logical to give moral value to creatures that cannot make moral decisions (that isn't to say I don't believe in some animal rights--but that's more of a reflection on what I think animal abuse says of the human involved than anything), but I don't really think we're going to see eye to eye on this no matter how much we debate the topic.