Deuce, what you're failing to take into account is signals. Each and every good has its associated signals. Your stomach growling is a signal that you need to eat. If you're having trouble fitting into your pants then it's a signal that you either need to purchase larger pants or hire a personal trainer or eat less or...
Who consumes public goods? Obviously the public. It should be up to the public to decide how much and which public goods they want. There's a huge amount of signals for all the public goods and there's no way that 535 congress people can observe and respond to all these signals as effectively as 300,000,000 people can.
Let's play a numbers game. We can say that each congress person responds to 1,650 signals. How many signals would each citizen need to respond to in order to outperform congress?
535 * 1650 = 300,000,000 * x
882,750 = 300,000,000 * x
882,750/300,000,000 = x
0.0029425 = x
Obviously each person observes way more than .003 signals. For congress to respond to as many signals as the American public is capable of responding to as a whole they would have to be nearly omniscient!