The "fantasy=escapism" equation is older than the genre as we know it. People in the old days boycotted the Theater, not just because it was a potential hotbed of wickedness, but because it was something other than Real Life and therefore odious to Sensible People. Some radical Christian sects have prohibited the reading of fiction on grounds that only the Bible has any literary value (....even though Jesus clearly told fictional stories).
In our day, fantasy as a fiction genre is more narrowly defined than simply "that which is not established fact." It encompasses stories of dragons, elves, dark and mysterious woods, magic (or majyck, or whatever the kids are calling it these days), unicorns, gnomes, etc. High fantasy usually takes place in a world or realm other than our own; low fantasy imports fantastic elements into the-world-as-we-know-it.
Certainly, there is plenty of fantasy fiction that can be defended on no grounds. The flood of worthless literary drivel with images of buxom maidens and swarthy sword-wielding savages with pointy ears on their paperback covers began sometime in the 1960s and has only increased as its putrid waters have swelled. But there's plenty of good fantasy, too, some of it among the best fiction ever written.
Because good fantasy, of course, has something to say about the human condition. Sometimes taking characters out of the humdrum of Earth-bound existence allows authors more artistic freedom to create the situations necessary to tell the narrative they have burning a hole in their imagination. Or sometimes they just make the story a bit more fun. Sometimes they make it darker, or scarier, or just plain more weird.
If you're J.R.R. Tolkien, the fantasy element plays a different role (mythmaking) than that of the story it frames (the sinfulness of sin and the cost of redemption). The point is, good fantasy isn't just about the fantastical. In most cases (Ursula K. LeGuin comes to mind), the unfamiliar is used to show how even it is ultimately familiar, and if we can see ourselves in the Edmund Pevensies and Gurney Hallecks we read about, the fantasy has done its job.
Q&A with Pastor Doug Wilson: "Should Christians read books with magic?"