Predation by free-roaming cats is a serious matter, and it deserves our careful attention ("House cats: the destructive invasive species purring on your lap," Feb. 25). The Humane Society of the United States values both cats and wildlife. Yet it is unrealistic and inhumane to simply gather up some 30 to 80 million unowned cats and remove them from the outdoors, as op-ed writer George Fenwick suggests. Adoption is not feasible for truly feral cats. Permanent sanctuary for that many cats would require inordinate resources. That means that the only practical way of reducing the population would require mass killing. That's not ethical, nor is it politically achievable.