By what logic are people predicting that Bitcoin will take a hit once the fork takes place?  The consensus here seems that most people will simply sell their BCC.  At least some of this money will go into BTC, which would cause the price to increase.

In order for there to be a decrease in BTC people would have to do the opposite.  They'd have to decide to start selling their BTC and go into BCC.

What I'm trying to determine is the following, please tell me what I'm missing:

Kraken is going to be depositing BCC in those accounts that hold BTC or who are long BTC with a margin position.  If someone were to take a margin position for 10 coins (~$27,000) prior to the deadline they would be given a free $27,000 in BCC.

If they sold bitcoin immediately they'd close their position without a gain or loss on the trade, but they'd have that free $27,000.  Even if BCC lost 50% they would end up with a free $13,500.   They'd take the risks that come with margin trades, but they would skip other risks related to having bitcoin on exchanges, etc, etc..   If they just bought BTC without the margin the math would workout the same way.

The only scenario I see for this backfiring is if Bitcoin were to take a major hit, which I think is unlikely due to a few reasons:
1. It's still bitcoin and the true believers are going to fight to keep it strong.
2. At least some of the free money will be going into BTC which should prop it up.
3. At least one exchange, Kraken, will be debiting accounts that are short bitcoin at the fork deadline
   ---- If you're short 1 bitcoin you will have an equal amount deducted from your account as BCC.
  ---This will force all Kraken users to close their shorts, which will essentially amount to a short squeeze.

It seems too good to be true, but I only have a rudimentary grip on this situation so far.  What am I missing?