Initial Coin Offerings are bizarre, fairly straightforward and can be fun.
Fun, well, that's a matter of taste so I won't debate you there.
But "fairly straightforward"? Let's not get crazy, here. IMO, ICOs are doing to cryptocurrency what derivatives did to traditional investing. Abstraction, indirection, and confusion, all to make a buck...
I've read a lot about ICOs and I still don't understand what's going on. I can't even tell what people are actually buying (like EOS, where it explicitly says the tokens are worthless and not convertible). An even bigger question is why people are throwing so much money on them when it's so unclear what you're getting.
It's a good example of a double pyramid scheme. The value of Ethereum is itself going up; it was worthless 4 years ago but now has a market cap of $20B. And then you can "spend" Ethereum to get additional tokens out of an ICO, which means that you're buying into another pyramid scheme with tokens which themselves have appreciated. The huge dollar values, after the double conversion, generate great news stories, which inspire more people to buy into Ethereum, which prop its value up even more, which mean that the companies who did ICOs can convert their cryptocurrency to dollars at better rates and inflate their dollar values even more, which inspires more ICOs at bigger valuations, and so on.
Lest this sound too dodgy, remember that all currency is itself a pyramid scheme: it's inherently worthless, and worth only what peoples' expectations of its future valuation will be. So the endgame for cryptocurrencies is either they run out of hard-currency buyers, in which case their value comes crashing down and everyone who bought in loses everything, or they replace the dollar as the world reserve currency and everyone who didn't buy in loses everything. I think the latter option is unlikely, but also underpriced, in the sense that it's more likely than most people give it credit for.
Here's a thought experiment... in the US, work full time while getting paid in Bitcoin. Make all transactions in Bitcoin. At the end of the year you'll need to file a tax return. Your final options are: 1. Buy some USD to pay your taxes. 2. Go to jail.
Demand for fiat currencies is ultimately underpinned by them being the only instrument accepted for payment of taxes.
You're driving at an important point that I want to take a bit further. Ultimately, the "backing" of a fiat currency comes from the barrel of a gun. People continue to use U.S. dollars because the U.S. has the strongest military on earth right now. Same throughout history - the backing of the British pound came from the British Navy, and when the British military collapsed post-WW2, the pound sterling didn't last much longer.
A major adoption driver for cryptocurrencies has been the weakness of central governments. We've seen this most with China, where wealthy Chinese businessmen are eager to take money out of the country in any way possible. But the most likely tipping point that would drive widespread adoption of cryptocurrencies would be if the perception became widespread that the U.S. government could no longer guarantee physical security; if, for example, we "lost" the war on terrorism. You could easily imagine people "hiring" personal drones or robots for protection with BitCoin if this came to pass, to fill the vacuum of the state security apparatus.
A pyramid scheme is one where there is a continued and ongoing transfer of wealth from new scheme joiners to earlier scheme joiners, which works great until the supply of new joiners dries up - then the thing collapses.
A new currency could work (in theory) absolutely fine with no further issuance, and no new joiners beyond the first round of adopters - not at all the same as a pyramid scheme.