Agree 100%.
I love these threads because I love reading the wacky justifications the economists of our community come up with...
Ahem. On behalf of economists, I shall respond to your gauntlet-toss.
The field of microeconomics, broadly speaking, consists of consumer theory and producer theory. In general producer theory focuses on profit-maximizing behaviour of firms. Consumer theory focuses on utility-maximizing behaviour of individuals. "Utility" can be thought of as happiness or satisfaction. I think when people are trying to discuss the economics of homebrewing, they focus too much on the production cost side and not enough on the utility side.
Once we understand that money is only one component of what gives people utility, we can understand why they would brew their own beer even if it costs them more than buying beer would. We brew because it (in general) makes us happy (as most of our hobbies do), regardless of the cost tradeoff between commercial beer and home brew.
So economists are correct in insisting that for cost comparisons alone, equipment, brewing time, etc. should all be factored in. But in spite of that, it's still rational to brew--it must be; we keep doing it!
I like to think of it this way: a Saturday golfing out of town somewhere would probably cost me $80 to $100 by the time I paid green fees, gas to get there, couple of meals, sleeve of balls, whatever. I don't factor my opportunity cost for my time into that so I don't do it when I brew, either. I spend a day having a blast making beer and at the end of it get 50 bottles or more to drink.