Sorry, but Cole's dialogue indicates that it was too late - the whole "Cold. Trapped. Heart hammering like axes on a carriage door." thing. I don't know about you, but it sounds like events were already in motion. That the axes were literally hammering at the doors, that he was hearing all of this and seeing it unfold. Again, Robert Chapuis - the man who hired Rainier - told him that it was just going to be the nobleman and some bodyguards (at most).
EDIT: For clarification, Blackwall says that he was told that it would only be the nobleman with bodyguards at most in some of his dialogue (unless I am grossly mistaken). I think the natural inference is that it was, in fact, Chapuis (the man who hired him) who provided him with what was clearly false information.
Again, he heard the children singing a nursery rhyme. He needed a second, literally one second, to scream "Stop!" to his men and the attack would stop. He could even tell his soldiers later that they had bad intel after falling back. But he keeps the attack going.
As for his position as a soldier and a captain? That has nothing to do with participating in the Game in my opinion. The only way to advance and grab power in Orlais is to play the Game; it might not seem important or significant to you, but to someone who is living within that society, it is. And if you're bad at the Game and screw up, you will be eaten alive, and you will face consequences for failure (probably death).
Still stinks that we can't stop the Game from existing in DAI.
Also, come on and be realistic here - Rainier was never a chevalier or a knight or whatever you think he was. Even if he had been a chevalier (he wasn't), well, chevaliers seem to get special dispensation even if they commit crimes like rape, and they can get off scot-free even when they commit worse crimes than that. Oaths of any kind don't really seem to mean too much in Orlais if you ask me. That being said, the old chevalier who helped him at the Grand Tourney was one of those rare specimens who actually did embody all the better qualities of chevaliers (as opposed to the scummy ones who abuse their power).
I am being realistic. I see him as a captain of the Orlesian military, which he was. Thus he was a soldier whose job is to protect the people of Orlais, not slaughter them.
The old chevalier saw something within Rainier and offered to mentor him, but Rainier was the c--- of the walk after winning the Grand Tourney (with the chevalier's help) and thought he had it all worked out when he was younger - so he spurned the man who could have taught him and molded him. Rainier was young and stupid and overly confident, not recognizing the value of what was being offered to him. Maybe you could say that that's when he took his first major wrong turn.
He lived to regret that choice later, but as he points out if you are in the romance, rejecting the chevalier's offer ultimately leads him to you. The fact is that the chevalier saw something in him, though. I think he saw the kind of man that Rainier could have been - alas, he made his choice for better or worse (mostly worse...and then better later on) and headed down the wrong path.
We really don't know anything about the chevalier that almost patroned Blackwall. For all we know, he was as bad as the rest of them. He was at the very least a murderer since the Chevalier initiation involves killing City Elves.
As for romance content, can't comment.
That's still just a matter of seconds before he has to make a decision. I don't know what kind of nursery rhymes you are used to, but the verses aren't usually that long. And his men may already have been on the move to attack. The people in the carriage are the last ones to notice the ambush. If we go by what Cole says (and since he can read minds, I think we should) then the attackers were already on the move. This is confirmed by Rainier himself when you talk to him in the cell.
He could call a retreat. And it only takes one second to do so.
I'm still not sure what you're arguing about. We already know that he knew there were children in the carriage and didn't stop the attack. If he had done so, his men would have known he was lying to them.
Literally no one is excusing him for this, so...
Well, he said he was told it was just the target and bodyguards, so he could say "We got bad intel" to his troops. He isn't lying.
Wait, so you think he's a stalker because he looks at a girl he likes but doesn't approach her? Maybe I'm missing some context here, but given how sunny and innocent Josie is, it makes sense to me that he wouldn't make a move.
I do agree that we shouldn't absolve BW of his actions. He choose to do it, and he probably had time to call it off when he realized what was happening. If you take those things away from him, you take away what makes his character interesting. He was a coward who tried to atone by becoming someone else, but that in itself was more cowardice and he hid behind it. He doesn't start really becoming the man he wants to be until he stands up and takes responsibility for what he's done. And even then, he has to live with what he's done. He has to be a man who would hate who he was without hating himself. He can't forgive himself, but he has to also get over himself..his atonement doesn't come from just righting wrongs, but accepting that he can be both a person who failed and someone who rights wrongs.
In the end, I liked that once he could admit who he was, he was less angsty. To me that was a big step for growth. He wallowed in that guilt rather than really face it.
As others said, from how other companions describe what he thinks and does, it is creepy.
He would have been more interesting if he actually did call the attack back, since he is an Orlesian soldier going against the Game, in my opinion.