It seems like this show is kind of love it or hate it, with a lot of people being displeased with the ambiguous ending.
That said, the events at the school are incredibly relevant to our times and it was a beautiful show of unity, bravery and friendship.
The ending may leave you frustrated and wanting answers (if you watch Brit Marling's other works, you'll notice a very similar theme), it leaves you with hope and challenges you to come up with your own answers and theories.