I mostly agree with aldo on the environment issue.
But it is human nature to be susceptable to believing and disbelieving something they have'nt seen or experienced personally.
The earth is not really that big. Near all astronaughts become environment friendly promoters after being in space. For the simple fact that they see and experience the size of earth. They see it as finite.
To some degree, similar feelings can be experienced after flying in a plane or being atop a tall mountain. The amount you can see from horizon to horizon. Seeing the curvature of the earth.
Its big yes, but not infinite. It has its limits, and without a doubt I believe humans have made a significantly large impact on the earths environment, and will continue to do so.
As for fusion. I think its potentially dangerous, yet potentially a solution to a lot of the worlds problems.
If the world suddenly had an infinite free, clean source of energy I don't think it would end up how you suggested Lib. It would still take several years for the plants to be constructed around the world, and at first it would only appear in developed nations.
Economically, its possible that countries that do gain it would at first gain International dollar.
Without power bills, more free money for the peasants to spend on trade, and thus more tax, thus more money for government. Needless to say inflation would probably catch up.
Fusion energy doesn't really solve the car fuel problem. Unless cars are switched to be rechargable battery powered. That however would require more years research and development. (The current ones are pretty crap) Plus more years for them to drop in price to be of normal cars.
Eventually the wealth would spread, and developing nations would get there own too.
The human race would learn to cope. There isn't much that could put us at a pause excluding the possibility of a third world war.
As for the government spending '****loads' on a potentially very advantagous project. How about the '****loads' they already waste on complete unrequired crap?
Anti-gravity. Hmm. Well I like to believe that nearly anythings possible so here's hoping.

But seriously, I'm a bit wary of strong electric fields and magnets. They say they are harmless, but I still reckon its possible to get cancer from those things, especially if you lived near one on a daily basis...
My 2 cents worth.