I have to agree that there is going to be a pervasive sense of lawlessness - it is a post-WWIII world after all. That doesn't mean that players should engage in wholesale rapine and pillaging just because they can, unless that's the kind of campaign everyone wants to be involved in. I think people should remember that while the T2K world is hard and brutal, no matter what miltary forces you're playing as, your characters are still (or were) professional soldiers and there's still some of that ingrained in them. After years of having the Rules of Engagment (ROE) and Law of Armed Conflict (LOAC) beat into my brain (so to speak), I'd have a very hard time in that sort of campaign.
As for being able to run that kind of campign, I think it would be a lot harder than people think for all the reasons everyone has listed before me. Additionally, with the hundreds of thousands dead soldiers through the course of the war, there's a lot of weaponry floating around. Any unit waltzing into a village to confiscate food or supplies, or to do worse, shouldn't be suprised when to locals commence firing on them with AK-74's. One nasty trick our GM pulled on us in a similar situation was to find the local villagers not only heavily armed, but using some damn good tactics against - most of the men were not only native to the village, but they were also part of the regional Polish reservist Army battalion. And the village wasn't just their home, it was their cantonment, and they sure fought like it. It just goes to show that if the players get out hand, the GM has ways of "helping" them remember that even in T2K, you're not necessarilly free to do whatever you want.
If a group is trying to play on the straight and narrow, but has a player or two who wants to act like Huns invading Europe, and the GM and players can't get them to take a hint, you could always roleplay a resolution as a last resort. In the last group I played with, most of us were current or former military members, so we played the campaign of soldiers trying to do their job despite the world they were stuck in. We had one player who joined us, and his goal as we later learned was to simply steal, kill and rape wherever he went. Eventually, after his character shot an elder of a village we were negotiating with for food and fuel because "he looked at me funny", my character knocked his out with a butt-stroke to the head. My character then assembled the village, held a summary court-martial for the offender and shot him on the spot. This was unfortunately something the rest of the playing group and GM had earlier agreed upon as a last resort. The character's player was, to say the least, not very happy about and after explaining to him for the hundredth time as to our style of play, our campaign goals and his constantly unacceptable playing style, he left in a huff and never returned. It was lousy situation all around, but the group was better off - especially since players who were drifting to that extreme during each session got the message. I'm not saying that our characters never did anything questionable or outright illegal, we just didn't make it the focus of the campaign, and afterwards everybody finally agreed on how we were going to play. While we did drive someone away, we could have easily just tossed the guy but we didn't want to lose a player. We were trying to get him to see that even in fantasy world, there are consequences and hoped he'd be part of the group, but he had his idea of fun and it didn't jibe with ours.
Long story made short, people can play any type of campaign you want, but the terrorizing raider campaign isn't really sustainable because: most people don't want it or can stomach it, most people get bored with it or because the GM and/or other players have myriad ways to show that it can't last or they take steps to stop it. Whatever you do, just make sure everybody's on the same page and have fun - it's a game after all!!!