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Yes because the Enigma protocol cannot accept USD, or DAI, so it requires an intermediate token. You can buy the ENG token with those other tokens but in order for the Enigma protocol to provide incentives across all platforms (not just Ethereum) it must have it's own token.

From my perspective it seems necessary. Why don't you think so?

Well, tell me how it is a utility and I will tell you where you are wrong.

Private computation is a novelty. Computation resources are represented by ENG, along with data, which in my opinion makes it backed by something and therefore a utility token.

So you say that it is a utility without saying what the token actually does! It doesn't make any sense.
Come on! It's innovative technology, let's get into technicalities here.