VAHEGURU JI KA KHALSA, VAHEGURU JI KI FATEH
There are a LOT worse things going on in Facebook than legitimate (married couples) putting up wedding pictures. Sikhs - Sikhi Saroop and Amritdhari - dancing, partying, relationships and the like.
You always have the option to un-follow a person if this disturbs you, unless you are afraid that they would be mad at you and not be your friend. But then, if you are befriending such people on Facebook (or have Facebook accounts), you knew this is the type of stuff that would happen on there, correct? It's not Nitnem - you CAN stop checking Facebook and delete your account and choose not to accept (and also unfriend) friends on there.
It's choosing to make a Sangat - you can (and should) be very selective as to who is on your Facebook and it could potentially turn into a Gurmat oriented environment if their mutual interests are Gurbani, Sikh history or Gurmat.
Also, I am encouraging every parent to have a Facebook account and track their children on Facebook - it can serve as a completely secret life that the parents may not be aware of, filled with temptations and unscrupulous people willing and able to take advantage of their children. Many youth are susceptible to insecurities and feelings that they are willing to express on Facebook and others willing to take advantage of, and the parents would never suspect their child unless they were monitoring them. If you keep an eye on them in the physical world, you definitely need to keep an eye on them in the cyber world - the two could be completely separate personalities.