No need for arguing really, this has a really easy answer:
The actual number of bitcoins doesn't matter. They are practically infinitely indivisible, and their price varies according to adoption and the size of the available market. Why would you ever need to change their number? It could have been 1, 10, 1000, or 1e56, it's just a matter of scale and price calculation for merchants.
The number of bitcoins does in fact matter for some of the predictions currently floating around. Take this statement for example:
The target value for bitcoin is 100.000 to 1.000.000 (
Source)
This is based on 2 assumptions:
1. Bitcoin someday will grab a 1% to 10% market share on the transactional currency market (600 billion to 6 trillion USD)
2. This market share will be fulfilled by 6 million bitcoins (around one in four bitcoins of the 21 million is actually used in transactions, the rest are in savings or investment plans)
Now if the 21 million limit changes, the outcome of the prediction changes too. Think of it this way: if you own 100,000 bitcoins and you know there won't ever be more than 21 million bitcoins, then you currently own 0.47% of the whole "bitcoin pie". Now if the upper limit changes to 210 million (thus the pie getting bigger), then your share of the pie suddenly shrinks to 0.047%.
It seems if the upper limit in fact is changeable, then the above prediction is not really useful.