Why do we cosplay?

[blinkyblues.livejournal.com]

Now my hater brother would like to know why do we cosplay? Why is it so prevalent in the Naruto fan community. How do we not see it as immature, for a grow person to dress up as a TV character? Seriously, it is my brother not myself that are asking these questions (as you can tell by the pictures in my other post.) I tried to explain it to him but I didn't seem to get my point across, so I am reaching out to the Naruto fan community to help him understand where we are coming from.