Why would it push the price up? Simple. Each mbtc would be sold for $1 and that would push the final btc price much higher.
The only way 1 mBTC would sell for $1 is if one whole BTC is *ALREADY* priced insanely high. So no ... your argument doesn't work.
We're discussing right now. When one mBTC is worth $x.xxxxxxx1.
We are not discussing 100 years from now when an mBTC is priced at $1.00
I want to know how it gets to that point.
Next?
The change to mBTC won't in itself change the value of Bitcoin.
The belief is that the general public is badly informed (not a bad belief).
As others have mentioned, the general public may think that you can only buy a whole Bitcoin.
You and I know this to not be the case but the general public don't know this so they don't want to plop down $700 for a Bitcoin.
Now, if you denominate things in mBTC, the purchase price now __appears__ to be $0.70.
Nothing has changed, however, the same general public will now feel it's much more affordable and buy up, say, $7 worth. Heck, some might even go as far as $70.
This opens up the market to the less informed people, resulting in more Bitcoins being bought.
Sure, it's not a huge volume but it's going to be some amount (the long tail).
It's this additional fiat flowing in that will increase the Bitcoin exchange rate. By how much is anyone's guess. It all depends on how many people believe that you can only buy whole Bitcoins AND it's the high price that's preventing them from buying.
Hope that explains things for you.
And at $1 it still won't feel expensive, gearing them up for $1,000 mbtc