Well, let's correct a few things there.
First, while there is a maximum of 21 million BTC that can be mined, each BTC is divisible to the 8th decimal place. Think of the Bitcoin as a 1 million dollar bill, and you can still break it into pennies. The "maximum number" is hardly more relevant than the amount of trees in the world that can be milled into paper currency before they "run out".
Second, the suggestion that BTC users would feel threatened by something like Amazon Coin is quite a dubious claim. The only real similarity they have is the use of the word "coin" in the name. Calling it a "competing currency" is just false equivalence.
Likewise, the "altcoins" such as litecoin and dogecoin provide many (or all) of the same features as BTC, but are more complimentary than competitive. R&D being put into one can benefit the others, and markets exist to easy convert between them. The ecosystem makes it very easy to participate, hardly what you would get from groups of people "attacking" each other. Trying different takes on the cryptocurrency process, putting theories through their paces, will ultimately make for a stronger ecosystem.
Finally, speculative value. Accept that this is a reality, and pretty much universal. Fiat currencies are based on speculative value as much as bitcoin is, the difference is that the fiat is more widespread thus the value tends to shift much more slowly. You accept a $20 with the speculative assumption that you can trade it later for something of equal value. Because it tends to have a lower volatility, this is considered a low risk assumption. Ask a Russian over 35 or so how that isn't necessarily true. Similarly, the USD has shown its own volatility, which has been overall quite negative, losing 95% of its value in the last 100 years.