There's an insinuation in that article from The Nation that the Army killed Tillman to prevent him from speaking out with Chomsky. I strongly doubt that the US army shot Tillman intentionally. The article says that Pat's mother confirms that this meeting with Chomsky was going to occur, but I have doubts about that statement in the article. Tillman was a free thinker but he wasn't a trouble-maker or a dissident in his past. He was a disciplined man who worked well within his college and professional football teams and I think he was unlikely to be planning any public statements with Chomsky. I also doubt that if he had set up a meeting with Chomsky, he would have told his mother about that meeting. I would think that a meeting like that wouldn't be important enough to bring up in a conversation with his parents. I'd like to hear his mother confirm that information in person.
Finally, even if he had set up a meeting with Chomsky and the Army knew about it, I doubt that the Army would have considered such a meeting to be a big problem for their mission in Iraq. I have heard stories about soldiers being shot by their commanders in Vietnam for disobeying an order, but I strongly doubt that Tillman was intentionally shot by any US soldiers.