Outdoor cats kill hundreds of millions of birds and small mammals in the UK each year. Balancing cat welfare needs with wildlife protection is a genuinely contested issue in conservation and animal welfare.
The outdoor cat welfare question involves a genuine tension between cat welfare and wildlife welfare. Restricting cats entirely indoors removes access to natural stimulation and territory - a welfare cost for an animal with strong outdoor instincts. Unrestricted outdoor access causes significant wildlife harm, including to already-declining species. The most defensible position is to balance cat welfare needs through enriched indoor spaces and safe outdoor access (catios, supervised time) while reducing wildlife impact through bell collars and dawn/dusk curfews. This is not a case where one side's welfare concerns can simply override the other.