Regarding population limits, take a look at this:
http://www.thepunch.com.au/articles/how-many-people-can-t...
"Take the world’s human population. We only made it to the first one billion people within the last 300 years. But then we really started packing them in. When I was born in 1963 there were 3.5 billion people. Now, just 47 years later, we’re double that figure and still climbing rapidly.
The question then becomes: how many people can the world support? There’s surely nothing wrong with 7 billion people, or 10 billion or 20 billion if everyone gets what they need to live. And there’s the rub. It takes a defined amount of water for each person to drink each day (a few litres for survival depending on local conditions) and the food we eat needs to be grown on land, the size of which is dependent on what we choose to eat. Air can be endlessly recycled but air quality needs to be maintained to keep it breathable.
Unfortunately the choices most of us make mean the consumption of more water than is available, the tilling of more arable land than exists on earth and pollution of the air to make it toxic to the hundreds of millions of people who have to breath it in the heavily populated megacities that are growing rapidly around the world.
The carrying capacity of the world is more than a simple question of how many people there are or will be. It’s the matter of how the resources of the world are divided among those people that is the current problem.
There is the concept of seven Earths: that it would take seven planets like ours to provide the resources consumed by the Earth’s current population if they all had the standard of living comparable to that of Australia or the USA.
The sad fact is we in the West can only maintain our standard of living at the expense of the rest of humanity. 1.6 billion people do not have enough to eat and half the world’s population consumes less than a tenth of all the resources used by humanity. We are quite literally living a fine life at their expense."
There is only so much space. There is only so many resources. And we are fast approaching the point where we will have far too many people on this planet. Keeping the murderers and rapists alive is not the answer, even if it is "cost-neutral".
http://www.correctiveservices.nsw.gov.au/__data/assets/pd...People do escape. And more and more people are going to escape if we do as you suggest and put murderers and rapists out into the community to work.
What % of prisoners are you proposing executing?
Every murderer and rapist. So whatever percentage that happens to be.