MTR Internet kiosks block facebook

I tried to access facebook in an MTR Internet kiosk. The connection was blocked and the alert message was that access to dating web sites was prohibited due to security policy. Facebook is a social networking platform with over 1 million Hong Kong people registered. People use facebook for a variety of purposes like exchange of messages, chatting with online friends, sharing of photos and videos, group discussions of a common theme, inviting friends to events and giving electronic gifts etc. I can not imagine why facebook should be blocked.