You're making a number of bad assumptions here. First, economics isn't a zero sum game. Second, arbitrarily increasing the total supply of money does nothing to increase total welfare. And third, the problem of an increasing population, i.e., more people consuming more goods, is a problem inherent in any system, and it isn't a problem that money printing addresses.

Here's what you need to know about money: all commodities are exchanged for other commodities; money is merely an indirect way of doing this which increases efficiency.

Not printing money and letting prices fall doesn't work either because it causes wages to fall.

You're confusing real wage and nominal wages. Falling nominal wages don't matter; rather, real wages can rise as nominal wages fall. That is, people can buy more goods and services with less money, though they make nominally less.

Sure, if the population increases, there's more people consuming the same amount of goods (if you assume that in one fixed point in time, population increases faster than production). Expanding the money supply doesn't change this because, again, all commodities are exchanged for other commodities.

Also, with a commodity backed currency--such as gold--you can indeed increase the money supply.

Manufacturers need to have some idea of what expenses they face in the future so they can plan ahead. Price volatility makes that difficult. If some material I'll need 5 months from now might then cost $1 a unit or $50 a unit, how can I know whether it's worth it to proceed? Thus there is a lot inherently positive about maintaining prices.

Given that the dollar has lost 96% of its value since the Fed came into existence, this argument is laughable. Prices are volatile precisely because of money printing. You're inadvertently making the case for a gold-backed currency rather than a fiat currency: you can only pull so much gold out of the ground whereas paper money can be created without limits (especially given our electronic age).

but then they do have to pay back the loan, so it's not like they're getting free money.

Except that, with fractional reserve banking, they've deposited their loan before they've spent any money to begin expanded operations. And when the bank receives the deposited loan funds, they can lend out 90% of that money, which in turn increases the money supply over and over again. So yes, the money is paid back, but you're missing the money that's created by other transactions.