You aren't gambling on anything. You continue to pay the price you agreed to when you bought the house. It's unfortunate if it ends up being worth less than you agreed to pay for it, but it's not gambling -- that's what happens when you buy a car, and buying a car is not gambling either.

Yes you're paying the same amount, for an asset that's worth a variable amount. The only time the amount that asset doesn't matter is if you plan to never ever sell it, which isn't realistic for most people (see elsewhere in the thread where someone pointed out that the median ownership time was 15 years or so).

What if you simply can afford to pay off the mortgage? If you can't, then buying the house was a bad idea no matter how the market moves.