Badly injured ferals, or those too wild to be retired to a captive colony, must be euthanized. For a start, vacated areas simply attract new cats. Also, there is a risk that indoor-outdoor pets may be caught up in the destruction. One of my colleagues lost her cherished elderly pet when it was mistakenly identified as a feral and destroyed. Since the frightened cat tried first to escape from, and then to bite, the SPCA officer, it was assumed to be feral.
Most feral feeders welcome trapping and neutering since they see so many cats die young.
In a few cases, the opposition to neutering is on religious grounds. The fact that ill or injured cats must be euthanized is a particular sticking point in predominantly Muslim areas of British towns. Neutering itself may or may not be permitted intervention depending on one's interpretation of one's religion, Muslim, Christian or otherwise. Modern methods of control involve creating smaller, stable colonies. Overcrowded colonies are unhealthy and may fragment.