"You really want more stability." But even if it is added to the benchmark S&P next year, it may not provide such a big gain for Facebook. While it may push some funds to buy it for the first time, there are a lot of institutional investors that have already bought into the stock, including Fidelity which boosted its stake by 20 million shares in the third quarter, when Facebook shares fell to nearly half its $38 IPO price. "This was a have-to-own stock for a lot of institutions, " said CMA's David Weild.