Ashitaka's quest is to "see with eyes unclouded by hate". Yet throughout the film we see eyes that have been quite clouded. The most literal example is that of Nago, who's eye literally spouts the demon hate worm (also, just realized that I've been waiting my whole life to write the phrase "demon hate worm" for a class) after Ashitaka shoots him. The other boar god, Akoto, has his eyes clouded by blindness, which widen and seem to see clearly only as the spirit of the forest takes his life. Blindness occurs amongst the humans, too. San's clay battle mask also obscures her eyes, regardless of how badass it looks, showing that she too can sometimes assume eyes clouded by hatred. Lady Iboshi laughs at the notion of eyes unclouded by hate, showing just how much stock she puts in the notion.
On a natural level, the points of greatest in the plot are often accompanied by slow, sweeping shots of fog-obscured landscape. Coincidence? I think not. While the film's environmentalist themes are most evident, it also drives at a more powerful ideal - absence of hate.