i suppose assuming the founders of the project are involved in some sinister plot to scam everyone is one argument.
They do not have to be in any kind of plot. >90% of the released ICOs so far are scams, this includes Ethereum ("Code is law".LOL). A platform that helps the creation of more ICOs, will naturally lead to more scams (hence my statement).
I think making sweeping statements about "greed" is a bit misguided and definitely feels like it has some passionate negative connotation behind it.
Greed, ignorance and stupidity. Those are the three reasons for which the crypto market is so highly inflated. Do you really think that people are buying Ripple (or were buying Ripple) because they understand the idea, read the Whitepaper and know how it works? If you do, then the most latter adjective would suit you. I mean, who in their right (and educated) mind would such centralized garbage? Oh right, nobody.