To be sure, the government does redistribute, but you would be mistaken if you believed this was all the government did. We don't have a government simply for that reason, we have it because it can provide certain things that the private sector either will not or cannot provide at all or at optimal quantities--things like police, firefighters, research, national defense, courts, infrastructure, schools, etc. These are public goods, and when you think about it, public goods are arguably the whole reason why we have a federal government in the first place.
As an example, imagine that a private company provided a road connecting two cities. The company's benefit from building this road is derived from whatever profit it can get through tolls and such. By contrast, the benefits to society are a good deal higher than the amount they pay for the use of the road, because the road is so instrumental to facilitating things like commerce and travel. Put simply, what this means is that because the private firm's benefits are lower than those of society, the firm won't build (provide) as much road as society would like. That's where the federal government comes in with road-building: it provides a useful, continuous network of roads and highways that spans the nation.
Yet today, we see many in the Tea Party and its associated off-shoots denigrating infrastructure spending by the federal government as wasteful. To be sure, it can be wasteful and excessive, just look at Japan! But as I've already shown, it would be wrong to assume that the private sector would provide the optimal level of infrastructure either. The only real way we're going to get the optimal level of infrastructure is if we make the government work optimally, not by retiring ourselves and our minds to the intellectual dustbin of boilerplate statements.