Would the attacks in Iraq increase or decrease if US forces continue to stay in Iraq?

increase definately as the Sunnis and Shias are fighting for dominance and control of the oil. The US is practically on the sidelines as it is now.

Many of the bombings are directed at Iraqis by other Iraqis

You must know that this could continue for years or even decades without the US even being there. This is why the US must stay. They must not stay so that they can prevent all of these attacks. They must stay so that they can get the Iraqis to be able to be competent enough to engage in what needs to be done.

Being competent doesn't mean attacks won't take place. Israel gets attacked all of the time even, throughout it's near 60 years of existence. But, I don't think anyone is going to say that the Israelis aren't properly trained and/or competent. Indeed, they are some of the best warriors.

But, even with the Israelis, it's possible to get a guy on a bus to blow it up.

We want Iraq to be able to last like Israel has. If we leave now, it definitely will not.

Plus, there will always be troops there. It is of strategic importance. After all, Iran is right next door and it is the biggest troublemaker in the region. Indeed, it is causing most of the bloodshed. Absent Iran, Iraq is pretty much a success.

I think it will be more of a blood bath then you are seeing right now, I know that maybe hard to believe but that is how I feel.