Anyone else hate the Maximoff Twins?

Tony is arrogant but not a douchebag. There is a profound difference.

A woman and three children still have their husband and father because of Pietro, and I think that's great.

Uh oh spaghettios - Zack Snyder, David Ayer, Bryan Singer (2016)

Their anger was misplaced, yes. But think of it this way:they're basically young adults who were mere children when their parents were killed. Most likely they'd known war all their lives and were numbed by it the way we are watching violence on the evening news. We care, sure, but if it hasn't happened to us/ours personally, it's a pale, distant horror. If a loved one is murdered and you can't find the killer...but you know the driver of the getaway car...what would you do? Misplaced anger, and its fallout, happens all the time.

Had the twins merely lost their parents to war, their anger might've found its proper channels. But they spent two days staring at the side of a warhead with Stark painted on the side, knowing its twin is what took their parents from them. Add to the fact that America is blamed in some countries for everything from hurricanes to split ends. So these two children are having to process their grief with the knowledge that Stark, an American, "killed their parents". It doesn't matter that Tony's father sanctioned making weapons to aid the war efforts, and Tony halted all war productions. These kids lived with this rage and pain and HURT for so long, it needed an outlet. And the scientists were only too happy to help in that regard.

I had more to type, but I run my fingers like I run my mouth, and I forgot not only what I wanted to say, but the rest of your post. I'm sorry...I blame it on being a gemini lol

No, it is a great example of how we know that they were basically brain-washed into believing Tony Stark and SHIELD were evil. Instead of getting counseling to help them deal with their loss, Hydra took their grief and twisted it.

They blame Stark because it was his bombs which killed their family instead of who used them. It is like blaming Remington for the bullet which killed your spouse, and not the scumbag thug who stole a gun and killed them.

The worst thing they did was mess with Banner's mind, but, again, they had been told a lie.

Once they found out what Ultron's actual goal was, they worked to stop him, including sacrificing themselves.

It isn't difficult to understand why the Avengers accepted them.