I am actually the admissions officer in a large state secondary school. Is it any less ethical to rent a house in the catchment of your preferred secondary school than it is to rent a house in the catchment of a particular primary school because it is a 'feeder' into the preferred secondary, and then to move back to your original home which is perhaps some 4 or 5 miles from said secondary, thus depriving someone who actually lives an awful lot closer to the secondary, but cannot get in because they do not attend a 'feeder'?
Is it any less ethical than it is to get a signature from your head of religion, be it priest, pastor, imam or otherwise, when you do not believe yourself, in order to gain a place for your child in your preferred school?
Or to accept military quarters which are smaller than your family needs in order to gain a place for one child in your preferred school, and then to move to a more suitable quarter, out of catchment, and thereafter use the sibling rule to get your other children in?
These things happen all the time. There are myriad ways to circumvent the system, and often the admissions team have no real way of checking. We cannot work on rumour and hearsay and even if other parents subtly try to grass up the offending parents, there is no real way to prove that someone has moved into catchment specifically for the purpose of gaining a place at a school, even when they telephone a month or so after offer date to say that they have moved house, oh and interestingly, it's quite some way out of catchment! It's a done deal by then.
I have thought and thought how to make it 'fair', but aside from dropping the 'feeder' school system, we'd be back to distance from school as the crow flies, and you'd still get people moving as close as possible just for the application process and then moving back out again. It would be discriminatory to specify a minimum residency in catchment of, say, two years, because then how to deal with children moving in and out of care, or military families, or refugees. So we are stuck as we are.
Of course, none of this would be quite as emotive if school places were not so over-subscribed in certain areas. If everyone who wanted a place stood a good chance, then people wouldn't resort to the trickery described above!