You mean PW, right?
Nope. PW is just a further "lets spell it out". The end of MGS3 already tells you everything you need to know. It tells you in one cutscene that Big Boss has changed completely. That he's lost all faith in the systems he previously was completely loyal to. At the begining of the game Boss even claims that he is so loyal to the President/ruling party that without question he would follow thier orders.
Yet at the end of game we see that Snake wants nothing to do with them. He won't shake thier hand. He's pissed off, the boss was betrayed by them in his eyes. Everything he believed is shattered.
It's pretty easy to see from there why he takes up the creed of the boss and does what he does in MG1 and MG2.
Or it would have had PW and PO not come in change things around, because at this point I don't even know what the character Big Boss is since PO and PW keep changing the characterization. And also changing what operation Snake Eater was. None of this for the better as things become even more convulated. After 3, everything was pretty simple.
But those things are already in older MGS games. I also never got the impression of him being some monster from the previous MGS games including 4. But then again this is a series that made the friendly people on your support team from MGS3 into the entire series over arching villians somehow.Sure a fallen hero, but really not a horrible person he's supposed to be by Metal Gear. If they took the whole child soldier + abuse thing with the normal MG tone I'm pretty sure this game would get A LOT of negative controversy.