They are an effective entity to allow state-actors a space in which to openly discuss matters relevant to them or between them and another state or states. They are also good at monitoring crises, allocating funds and aid to areas in need, as well as providing financial aid to those states who need it. What people seem to get tripped up on is their security enforcement. The UN, alone, is not and was never meant to enforce their resolutions via force. This comes from the state actors within the UN who so choose to enforce these laws and norms. This is why the UNSC passes resolutions authorizing the use of force; those states who do choose to use force to punish a state are doing so legally and not breaking any international law by doing so. The ineffectiveness emanating from the UN (or rather, the UNSC) is the veto power that the five permanent members have. As seen with Syria or Crimea, these states can veto resolutions that they feel undermine their interests. However, that being said, they are not a pointless organization. In an anarchic (no central government not chaos) system like how the world operates, the world needs an international institution to provide some sort of obligations, rules, and norms that states should abide by.