Is a garbage disposal an environmentally friendly home appliance?

No, many people use it as a garbage can and put a lot of food scraps down the drain. There are areas in the US where this is suspected to be the cause of water ecosystems being damaged. All water that goes down the drain, if it isn't a septic system, is treated and released back into rivers or other natural water systems. The added organic material from food scraps is creating an unbalance of nutrients in some water ways and can kill water life.

The other thing that makes it non eco friendly, is it uses electricity, and the task can be accomplished with minimal human power, just scrape your scraps into the garbage.

You still have to use electricity and this inorganic material that is produced and flushed into the sewer lines only to rot. A simple compost is beneficial to the environment and loam for a garden or simple put back to earth as a positive building block. Even if the food stuffs were put into regular household garbage disposable and back to the landfill is healthier to help break down all the plastic and waste, even thought it will take 20-50 years to decompose.

It is the second best choice, with the first being composting. But if you can't compost then yes, as long as you don't have a septic tank system which may cause problems with lots of food disposal.

No the disposal is not green friendly,they have linked water problems to disposals (high level of bacteria)

Not really. If you think about it, it's the same as throwing food away. Some may beg to differ though.