You can make a horribly inefficient tool, but if it relies on green energy and uses green materials then it does not particularly matter how inefficient it is. It is a multiplicaiton issue. 0 X 1,000,000,000,000 = 0 and there is no way around it.
So yes, lets look into greener sources of energy and materials for the sake of being green. But let's look into more efficient printers for the sake of production capability.
The big issue with 3D printing is that it is far too slow for proper mass production on objects that can be injection molded or easily sculpted and welded into shape. Those operations can be done quickly and accurately, and in batches of tens of thousands of products. 3D printing is good for smaller batches of custom parts, large objects like buildings and airplanes which would normally require a lot of individual parts, and complicated objects with a lot of moving and/or embedded parts. It is great for bowing because airplanes can be made of less pieces, with lighter weight, less screws and maintenance, etc. It is great for joe consumer like myself because I do not need to drive to home depot to buy a single molly to hang a picture, and I can make custom lightswitch plates for my kid's rooms, custom legos for my son, and dollhouse furniture for my little girl. I can make custom cell phone cases, and if I ever get so complicated as to adding electronics then I can make custom docking stations for devices and cable connectors. The list goes on and on and on for fun things that it is useful for.
But if I was starting up a company, and I wanted to sell a few million game consoles it would be horrifyingly and frustratingly slow to 3D print all of those console cases, controllers, and accessories. It would be inefficient beyond belief! But if it was green or not depends on the type of power and materials used, not the quantity of time, power, and materials required.
I don't know any better way to sum this up, other than to say this is dumb.
Society is growing, and needs new ways to support itself. Efficiency is the goal of production. If you make something efficiently, then that means you used the least amount of resources possible. If something is artificially cheap because of taxes or corruption, then adjust the price.
Its like trying to argue that horses are better for the environment than cars, because both can be used for transportation. Now, imagine life in NY where all cars were replaced with horses. Supplies would not be able to come in fast enough, and food is a major supply. That would mean people would either have to move out or starve.
The biggest problem with manufacturing is that it has to support a massive population. Everything has an impact on the environment, and only "nothing" has 0 value. If a 3D printer can produce something with less waste (waste being subjective) then great. If population then increases, then any change in efficiency is washed out. The world cannot support its population with its current production methods. Either increase efficiency, reduce population, or a mixture of both.
Number 1 rule about environmentalism is adjusting the demand. Make us consume less.
You cannot supply infinite demand with finite resources.
People always think , environmental problems will be solved by some miracle technology. It wont be.
Why that much plastic is needed at first place? Why we need so much cars? ( instead of sharing, cycling and walking)
After demand has lowered to a manageable value, than you can start talking about efficiency. In a World with no one changes its destructive consuming lifestyle, no amount of green-tech can save you.
That is the very problem. You should never stop thinking about productive efficiency. The best thing for the environment is efficiency. People confuse efficiency with the ability to make more even if it hurts the environment more which is wrong. Most people are for "helping" the environment as long as it means they don't have to change their lifestyle. Do you really NEED to go online and post a comment? Would it not have been better for the environment had you planted a tree? Instead you surf the web, driving up demand for computers, using electricity and increasing your carbon footprint. Technology is the only way we can hope to decrease the impact of our lives on this planet, because we simply don't seem to care about driving down demand.