Is there any good reason not to distribute StarCraft replays -- like maybe security or something like that? For that matter does blizzard or battle net have a social area that they maybe allow public download/viewing of replays?
One of the biggest reasons that players do not want their playstyles to be found through people watching their replays. One of the biggest weapons you have against your opponent is the guessing game of what build order you use on what maps. If you tend to use a certain strategy on a certain map then your opponent can blindly go with a counter build and just win, simply based on your habits.
That said, players sometimes do release replay packs to their fans.
Blizzard themselves do not have a social area for the upload/download of replays but there are a few sites out there:
You'll need to download the replays and then open them up in Starcraft 2 to view yourself.
There are no security issues. AFAIK a replay includes only your screen name, but not your unique number. This way no one knows your real account or can add or harass you ingame.
Some players do not like their replays to be public, here are a few reasons: