Just to follow on my previous albeit brief comment with some more explanation:
It's not a Ponzi because new members are not paying for the old members. If anything it is the other way around.
Money is coming in from the outside though in the form of Bitcoins which are being used to buy and speculate on STEEM.
Even if people think it is a scam (which it is clearly not) it is inaccurate to call it a Ponzi scheme.
This "Ponzi" slur is used by everyone to describe any kind of financial endeavour which they don't understand and/or they were too late to join and hence feel they are missing out on.
It happens with some companies which suddenly make it big and surprise people, it happens with some investment products that get a lot of attention and it also happens with a lot of cryptocurrencies including Bitcoin which continues to be labelled a "Ponzi" by antiquated people with vested interests in the "old system" of money.
The only thing that this inaccurate use of the word "Ponzi" shows is the fear and lack of intelligence of those using it.
They are unable to accept that something genuinely important or useful may have missed their attention and so try to slander it and hence sabotage it to confirm their own prejudices and deny their own ignorance.
Ignore these people because they are too entrenched in their own ignorant biases and self importance for their advice to be of any use. Once something like Steemit becomes firmly entrenched and established they will probably start pretending that they saw it and predicted it all along.
That is how these kind of people operate.