It isn’t inherently bad -it’s the Seviva. Take a hall in the middle of the city -it’s just a hall. Add a rock band & add Goyim dancing not wearing Tzinus clothing and I won’t mention what else. Now a Jew doesn’t belong there, even if they are doing something Kosher like a Shidduch Date, because it’s a bad Seviva.
Do you know any really Frum guys who would take dates to a disco place? I don’t think so. Facebook is the same thing, just in the privacy of your home.
Not a good analogy. In the same building as that hall you mentioned, there is another hall. That hall is totally kosher and totally tznius. Only invited guests are allowed in.
Facebook is the building. You choose which hall you enter.