Justine is actually the villain of the Film and here is why...

...she betrays Daniel by not telling the truth as to what really happen. The guy jumps into the river to save her...he does whatever possible to escape with her and in the end he is brutally killed by the savages with the ants.

It don't matter whether you side with the tribe or the logging crews. There is no reason for THAT KIND OF BETRAYAL. Sure Alejandro is the a-hole but not the villain. Justine hid the truth to protect a bunch of cannibals instead of exposing a DANGEROUS SOCIETY.

You can say the cannibals were following their traditions. You can say the loggers were doing their jobs. You can say the college kids were passionate about activism. But to say Justine is not the main villain? Nope.