People believe bitcoin is backed by nothing. I think that is not the truth. I believe bitcoin is actually backed by people themselves. It is backed by none other than just you. We all witnessed the price has been fluctuating by all those FUDs and bad news. The price changes by emotion and non logical facts. I believe you hold bitcoin no matter what happened and would happen, and believe it is backed by all of us, it would make a history.

Bitcoin supported
1) money idealists who believe that bitcoin will be able to defeat the banking system and become a new world currency.
2) money traders who have brought their money to the stock exchange in an effort to earn and buy bitcoins from miners and other traders. (This includes except for single traders and financial funds)
3) companies producing asiki, since if something happens with bitcoin, they will actually go bankrupt because ASIC can only consider Bitcoin hashes.
4) companies that act as merchants. That is, they allow shops to sell goods for bitcoins, while the store will receive payment in rubles / dollars / euros ...
5) illegal operations with money laundering / drug sales and other. Silkroad and analogues.
In general, some ecosystem has bitcoin

If I did not name any spheres, then maybe someone else will add.
I want to add electricity to your list. First of all, the cost of cryptocurrency supports the cost of electricity needed for its production and maintenance. The bankers and the government spread many different rumors to create a negative image of cryptocurrency.