Sometimes it bugs me how often Yahtzee can give biting insights, and other times he can miss a huge amount of the point almost entirely. Sometimes I thing he's just sounding off for the sake of sounding off.
I'm not a huge "Gears Of War" fan, but understand that we're dealing with characters who are career military, and a protaganist who is a hardened veteran before the game even starts, and has also done a fairly notable stint in a military prison.
Military training by it's very nature is supposed to strip away most signs of emotion and individuality, the idea being to replace everything you are with something better... well better in the context of killing people and breaking things in pursuit of a goal someone else decides on. Soldiers who recognize the enemy as having valid points of view, or being regular people with lives and families are kind of useless in reality. All arguements about politics and morality, when your fighting to win soldiers who pause to contemplate the inhumanity of war and what they are doing to their enemy in the midst of a battle can't do the job. The last thing you need is for the guy standing there protecting you to pause and go "OMG, I can't kill this poor unfortunate" while that guy proceeds to kill him and then turns around and massacres you and your entire civilization.
We could sit here and argue about the morality of this entire thing, and the nessecity of it, but I doubt I could do a better job of explaining it and WHY it's needed anymore than say Heinlan's "Starship Troopers".
When looking at a game featuring the military, especially characters who are supposed to be experienced veterans... yes, they are going to be fairly uniform. That's actually good writing since this is what the system produces. Take one of those guys, toss him into a military prison where emotion is a weakness (prison can be very dehumanizing on people who want to survive it, especially military prison), and then toss him back out into an apocolyptic war... and yeah... Marcus Fenix is pretty much what your going to get. If he was any other way it would actually have been bad writing given the backround which ties into the entire thing.... and this is a defense being made by someone who doesn't paticularly like the game in question.
Simply put the whole "Macho" attitude we see here, is kind of realistic for the kinds of characters we tend to deal with. In general people have differant mechanisms for turning out that way. Joking about everything and becoming a sort of macabre clown who takes nothing seriously while doing their job with lethal precisian, or becoming the aloof "Marcus Fenix" type are both very typical ways of dealing with this kind of life.
As far as cutting down bad guys who have legitimate points of view and/or justifications for what they are doing, that's pretty much reality. In general nobody wakes up and decides "we're going to be really evil today just for the heck of it" everything happens for a reason. Of course the Locust/Chimera/Muslims/Whatever have legitimate reasons for doing what they are doing from their own perspective, some of which might even seem fairly reasonable to the other side, if they didn't there wouldn't be a massive scale war. This is incidently exactly WHY you dehumanize your soldiers and strip away a lot of their empathy. In the end pretty much all wars come down to "us or them", "my side, and their side", the bad guy and the good guy are all matters of point of view, and when it's come down to a war only one side is going to be left functioning, and that's the side that gets to record history.
A situation where a bad guy goes off about how legitimate their cause is and then gets cut down by some grunting soldier who might have a personal vendetta is pretty much a summary of war in a nutshell. In the end the point of view of the loser doesn't matter, it's all about who wins.... and in "Gears Of War" it is very much an "us or them" type situation no matter who might have the overall moral high ground when you scrape all the muck away.
Honestly from what I know of the series "Gears Of War" set out to make a sort of commentary on the nature of war, and really from the plot points I've seen it's done a fairly good job of making the points it set out to do. Marcus Fenix might be stereotypical to some extent, but I suspect that's kind of the point, as is the simple point that once a war breaks out
the reasons behind it no longer matter, with it being the job of a soldier to end the war favorably for their side or die trying.
But then again, the realities of war have never really sat well with the left wing regardless of what name it uses in a given country.