I haven't insulted anyone else. Or you. At a push, I've insulted what you say.
"I'm also not happy with banking on loads of people dying from wars/disease to save us having to solve it." Well, tough. Either there are too many people or there aren't. If there aren't, then the real problem, far from being lax border controls, is that we are not doing enough to redistribute wealth. If there are, then some of them have to die. Either this happens coincidentally, or we kill them.
Personally, I am confident that the planet - and, indeed, Britain - can support many more people than it does already. Population, like it or not, is largely self-limiting in response to available resources. But this increase (which is inevitable if we keep living longer) can only happen if we start sharing wealth and knowledge in exchange for land and resources.
It is ultimately likely that the concept of a nation state will become outmoded and preposterous. Until it does, you must expect people with less to be attracted to what we have and to try to get some of it.
But really, pinning our hopes on returning to a society where we attempt to be self-sufficient - have you actually given this any thought? Where is the coal and oil going to come from? If from abroad, we'll need to export sometihng to pay for it - what will we have if we're all busy making our own clothes? Where, given our climate, is citrus fruit going to come from? Who is going to move into high-rises to free up the extra arable farmland and grazing we will need for basic crops and livestock?
I like a good debate as much as the next man or woman, but please, if you expect to be taken seriously, say something serious.