Hi Josh,
The problem here is not that people think that MobileCoin is not a useful technology or is not innovative. From what you are describing it actually seems like a good combination of features that are particularly suited for the messaging use-case.
The problem is in the way the coins were pre-mined. It seems (we don't really know from the outside) that the knowledge that Signal would be using MobileCoin has been known early on. With that knowledge it is very easy to make money by pre-mining coins. The proper analogy here is insider trading. It is immoral and that is why people are calling this a scam.