For example, it might result in uncontrolled population growth, with the remaining wild environment being destroyed to accommodate them and their food needs. Security achieved at the cost of most of the remaining beauty in the world, and people dehumanised, living like maggots in an angler's tub.

That's a classical Malthusian viewpoint. Trouble is that it doesn't reflect experience in the West. We have more available power, cheaper raw materials and cheaper food than anyone else anywhere in the world any time in history. The result is births below replacement levels in virtually all Western countries, and in most countries that are at or above replacement, the cause is from immigration and children of immigrants.

It's pretty simple really. If you know most of your kids are going to die young, you need to have lots in order that some will survive. If you know that it's 99% sure they'll survive, then you're better off (and your kids are better off) if you have a more targetted approach to child-raising, so that you choose to have them only when you have the resources to support them without significant compromises on their (or your) quality of life. Certainly there *is* uncontrolled population growth as cultures adapt to fit the new environment - historical population graphs show something like a tenfold jump in the 1800s as increased food supplies and improved medicine took effect, whilst people were still having a dozen kids - but over time that levels off. There's a grim irony in the fact that the developing world today might avoid the problems of that jump because of AIDS.

As far as fusion plants go, it's still using a finite resource - there's only so much deuterium and lithium going around. But estimates are that it's enough to keep the world going for a very long time, so not such a big deal. Useful link including brief info about the reactor itself becoming radioactive.

Graham.