Even people who only want to get rich quick still contribute to the network. If they buy Bitcoin, they increase its price, and higher price means more hashpower for mining, and more hashpower means the network is harder to attack. So, without the "get rich quick" people the network won't be as secure as it is now. Also, traders provide liquidity, which makes the market healthier, and everything that is good for the price is good for the network. Also, the more people use Bitcoin and do transaction, the harder it is to spy on everyone.