The new regulations recently proposed by the European Commision can result in fines of up to 2% of revenues. Not profits, revenues. That's not puddly by anyone's definition.
Additionally, the EU is perfectly willing to prevent EU companies from dealing with non-EU companies who don't comply. If FaceBook doesn't have EU advertisers on their system, all EU users suddenly become a drain on FaceBook resources for no gain. Yet if they leave the market, previously 2nd-rate competitors (such as Google+) get a huge surge in Europe, which may / will help them break into other markets.
In the end, FaceBook will comply.