Quite frankly, there are mountains of evidence for the former proposition while most of the evidence for the latter proposition hinges on only looking at half the equation.
Just to name perhaps the two most prominent examples for the "government is a force for good" way of thinking: Social Security and Medicare are certainly popular government programs, so popular in fact, that few conservatives would be willing to support ending them. However, the financial strain being created by those two programs is on track to bankrupt our country in the next 20-30 years. If that turns out to be the case, then all the good done by those programs will be very small indeed compared to the cataclysmic damage that they'll do to our nation. Now, is it possible that those horrifying consequences won't come to pass? Certainly, but the nation will have to be practically sliding into the abyss for the politicians in DC to risk seriously tampering with those programs. Thus we cannot, and should not, ignore the tremendous harm that even wildly popular government programs can potentially do to our country.
On the other hand, the best evidence for the "government is a necessary evil" school of thought is that almost every extremely serious problem our country has dealt with in the last 75 years has had at its root, actions taken by the government.
The Depression? It was an economic downturn turned into a lingering disaster by the government policies designed to fix it. Gas lines during the Carter years? That was caused by government price controls. Staggering out-of-wedlock birth rates? Welfare and no-fault divorce laws created that issue. A flood of illegal aliens? The government failed to secure the border and deliberately refused to enforce the laws. The mortgage crisis? The government forced businesses to give loans to bad risks. The deficit? The government spends too much year after year after year. It goes on and on, but you ALWAYS, ALWAYS, find government actions at trouble's core.
So, how does the government get by with this? By pointing out the good a policy does, or more often than not, the potential good it can do, while studiously ignoring the costs. As Thomas Sowell is wont to say,
"Killing the goose that lays the golden eggs...is a viable political strategy, so long as the goose doesn't die before the next election and politicians can avoid leaving their fingerprints on the weapon."
That's not to say that we should NEVER rely on government. If that were the case, it would simply be called an "evil," not a "necessary evil." Sometimes there are tasks that the government is best suited to take on: defending our nation, delivering mail, building and maintaining roads, regulating industries, breaking up monopolies, etc.
But even in these limited areas, the government often does a poor job. We have bridges falling down because of poor maintenance. Our government does a mediocre job of securing our borders. The customer service at the post office, DMV, IRS and other government agencies is often poor, and regulations are often written to benefit companies that give the most campaign contributions to the government.
There's a lesson there for those that are willing to hear it. Whenever someone claims that government is the answer, your antenna should go up, you should make sure your wallet is safely secured, and you should evaluate every statement that person makes as if it were made by a professional con artist serving twenty years in a federal penitentiary. Then, and only then, are you ready to decide if the government should become further enmeshed in the lives of Americans.