Honestly, it just depends on if the person can "see through the veil" as I call it.
For many years, my confidence and belief in the armed forces was unshakable. I was raised military. Wanting to be military was my entire existence. I remember playing some naval warfighting game on a Super Nintendo when I was young and my dad would be deployed, as I would pretend that I was also military. Years later I was awarded an ROTC scholarship and got into all of the top military schools I selected. I completed the ROTC proram as one of the top candidates in my class. I got voted the, "Most Motivated New Officer" and "Most Likely to Become a General/Admiral" by my peers. The military was my identity - the rock on which my most core values and ideals were shaped. There was literally nothing you would be able to say that would be able to convince me that the US wasn't the throbbing cock of justice in the universe and that the Marines weren't valiant warriors fighting the good fight.
One day I woke up, and for whatever reason, a switch had flipped in my head. I realized that I had been brainwashed and that much of what I believed was a lie. Who I was came crashing down. As I came to terms with a numer of the points in OP's post, I became deeply (clinically) depressed. I scored a 19/25 on the depression screening they gave me on base (the missing points were because I had no desire to hurt myself or anyone else). I would often cry myself to sleep at night
How prevalent is this opinion? That is hard to say. Of course I will hold the view that I am right, but I think everyone who has served (especially in a combat zone) will hold it...I just don't think that all of them have realized it yet. Some of us out there hold it, recognize it, and may even talk about it....but from personal experience, I wager that the majority of vets, when they look into the mirror, will never be able to confront the notion that who they are/were, what they stood for, and what their brothers and sisters died for - was a lie. We weren't the good guys...we aren't the good guys...and for each of us who signed on the dotted line, it is OUR FUCKING FAULT.