As a business, it will always be a bad idea to completely rely on another entity outside your control, whose interests are very likely to be misaligned to yours. By all means leverage, Facebook (and Twitter and others) sign on and APIs, but if you are building a business on a single one of those, you are completely at the mercy of their whims, any incompetency, and changes in business practices.
There are always risks in business. Are all the people who have built successful companies that rely on facebook, apple, twitter, google, or other platforms wrong? The important thing is to understand the risks and account for them. Don't overreact just because having your app suddenly pulled seems more traumatic or less under your control than other failure modes.
And a game of three-card-Monte involves risks(http://en.wikipedia.org/wiki/Three-card_Monte).
How do you distinguish the risks involved in one from the risks involved in the other? I'd say one important question is whether the "house" has more incentive to take your stuff or more incentive to benefit along with your success. Considering that Facebook's business model is essentially still up in the air, the question of what Facebook in particular cares most about is also up in the air.