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Iam well aware of Metcalf’s law, however in an open system such as Steem where Steemit is not the only function operating on the Steem blockchain, an increase in users alone will not drive the price higher.
In fact, if some tip named youtubers joined Steemit, they will be withdrawing their earnings putting downward pressure on price!

Withdrawing doesn't drop price. They could sell it, but for every seller you need a buyer. So yes please, let them sell! All that does is to increase the trading volume of Steem - once again increasing price.

More sellers than buyers drops the price! Simples.

I think you're grossly underestimating the effects of increased liquidity and awareness.