monty is comparing wild to captive.. zoos are not trying to breed the lions to release. They are trying to breed to build up numbers. Culling males would go against this...
There has never been a zoo or hand raised lion successfully released.
The famous ones which were released are Elsa and her cubs, but they were not successful. Elsa was shot after killing and eating a guard meant to protect her. One of her cubs was shot after killing a child and another was shot after it became a cattle killer. The other disappeared and was probably shot attacking cattle but not reported. The recent one "the Harrods lion" also disappeared after a year.
There is a program in Zim at the moment where they are teaching captive lions to hunt, with the plan being keeping them in a several thousand acre enclosure, where they live naturally and then release their cubs as they will not be humanised.
Australian Lions will never be released as they are a mixture of bloodlines. Here they are for education and entertainment, as they are a good crowd puller, which through gate takings increases the earning power of zoos, keeping them viable.
My point is that more breeding will help keep the Australian population viable. Keeping large numbers of males which will probably never get the chance to breed is a waste of resources and an expense zoos could do without. Small zoos such as Mansfield which house 2 males are a better option as they gain crowds and gate takings due to the Lions and make it necessary to kill excess, but these places are not always available. In the long term it may pay for the larger zoos breeding Lions to help small places such as Mansfield pay for their enclosure, as this will take excess males off their hands and free up their resources.
Mansfield's Lions are also 12 so in a couple more years the will be after a couple more.
Killing any excess should not be the first option but there is no reason it should not be an option when necessary.