Let's begin with Half Life 1, shall we? It's pretty straight forward, after all. All Freeman really does is look out for himself while SPECTACULARLY failing to prevent an alien invasion. That's...pretty much it. But then, in Half Life 2, he's somehow become some sort of fucking Messiah. That obviously makes no sense, but whatever. Maybe retellings of his actions have been exaggerated over the years. But by the end of Half Life 2, that excuse is rendered moot. Let's examine all the results of Freeman's actions:
1. Within hours of his arrival, Freeman successfully leads the Combine to the Underground Railroad, effectively destroying the Resistance's only method of getting people out of the city and leading to a LOT of dead Railroad guides. Remember this one, it'll be important later.
2. He then leads the Combine straight to Black Mesa East, destroying their primary base of operations and leading to Eli's capture. Now, you could argue that The Combine already knew the location of Black Mesa East thanks to Mossman, but then...Why didn't they destroy it earlier? And they weren't still trying to steal the Resistance's teleport technology, since Freeman finds a functioning teleport in Nova Prospect just a few hours later. The Combine had no reason to wait, therefore, they can't have already known the Resistance's location, and THEREFORE...Freeman led them right to it.
3. He manages to get all the way to the Combine center of operations and what does this MIT graduate do? He starts banging shit together at random, resulting in an ENORMOUS explosion. Now, I know what you're thinking. "The Combine caused that explosion to open the portal!" No. No they didn't. They just took advantage of the situation to open the portal. In other words, they didn't actively cause it, they just didn't fix it, either. Now, the effects of this Freeman-caused explosion are so far reaching, they get their own separate number.
4. Obviously there's gonna be massive casualties from all the citizens that weren't able to escape the city, but it's actually even worse then that. The people that DO escape have no idea where to go, thanks to the collapse of the Rail Road. They'll probably die out there in the wilderness. And even the ones that somehow reach a Resistance Base are screwed. Think about it: Before Freeman got there, the Resistance only ferried people out of the city a few at a time. Now, they've got THOUSANDS of new mouths to feed, and a Combine that's on the offensive. Where the fuck are they going to get the resources to deal with that? They can't. Freeman didn't SAVE the citizens of City 17, he DISPLACED them.
Gordan Freeman: Saving everyone, even if it fucking kills them.