“Dreams are necessary if one is to hope, but they are also dangerous. How is this statement true for the character George?”

This dream, I think, is the American Dream.  Before the
Great Depression, this dream seemed real: even immigrants who didn't speak English could
dream it.  This dream was based on a strong work ethic.  But now, in the midst of near
famine and economic upheaval, this dream seems no longer true.  A strong worth ethic
alone does not achieve it.

George and Lennie, no matter how
hard they work, will not achieve their Dream Ranch.  George, in this quote, I think,
knows it.  He knows that the earlier American Dream is a false one now.  It is the dream
that lures thousands to the promised land of California only to disappoint them, leave
them homeless, and destroy their families.

In California,
there is simply too much competition and not enough workers' rights for this dream to be
valid any more.  The dream is only valid for the bosses (The Boss and Curley) and not
the workers (Lennie, George, Slim, Candy, Carlson, Crooks) or the minorities (Crooks) or
women (Curley's Wife).

In short, The Boss lures these
migrant workers to his ranch in search of a dream and hope, but--in the end--they only
find lice, abuse, cruelty, and death.