What's the theme of the poem?

The overall theme of the poem is the equal destructiveness of hate, or "ice," and desire, or "fire." Frost introduces what seems like a long-standing debate concerning which is the more destructive:

Some say the world will end in fire,
Some say in ice.

But Frost is adamant that this is not a matter can ever be resolved to everyone's satisfaction. Many people have had their lives destroyed by hate; one only has to think of the many savage wars that have plagued humanity since the dawn of time. Yet at the same time, desire can also have extremely negative consequences, whether it's sexual desire, desire for money, or desire for power. In both cases, we are dealing with forces that cannot be completely comprehended by the limits of the human mind. All we can reasonably do is to recognize that hatred and desire are both equally dangerous and try our best to bring them under control.
https://www.poetryfoundation.org/poems/44263/fire-and-ice