AFAIK it takes 5 minutes to fork Bitcoin and create a new altcoin. Why would I use ethereum for my altcoin instead of doing a new altcoin?
Here is the tutorial about creating your own coin on ethereum. It's pretty short and interesting: https://www.ethereum.org/token
People like to think of ether as another cryptocurrency like bitcoin but the ethereum currency is intended to be more like a commodity that is used to fuel the platform that runs all sorts of stuff (including currencies).
> A bitcoin fork means you have to build up a group of miners sufficiently large and diverse enough that everyone trusts it.
Of course, you need miners. However the mining is the easy part, otherwise you need marketing, use cases, etc, for the currency to get any traction. I think an altcoin working on top of the ethereum blockchain would not be as convincing as invidual altcoin.
However of course if we are speaking about some other kind of asset, it might make sense to do it on ethereum.
> Making a currency on ethereum means it inherits the trust that ethereum has.
No. Maybe mining security or something, but trust? Why would anyone use these crappy in-ethereum tokens, when you can just use ether itself. Or bitcoin.
You can make tokens as well inside bitcoin via colored coins and similar methods. They haven't gained much traction, I doubt that they will inside ethereum.
The developers can focus entirely on their business use case for the currency (and the marketing) without the need to create an entirely new cryptocurrency.