I generally think that the way in Iraq was a mistake; however, even then:

The motivation appears to have been different, fighting terrorism and finding WMDs versus societal control and religious intolerance.

The majority, though certainly not all, of the people killed were combatants rather than civilians.

No, the majority were ~innocent people. Although, as in any invasion, the distinction was blurry.

While the invasion was sold on the basis of terrorism and WMD, that was mostly bullshit. I mean, the US originally supported Saddam Hussein because he opposed communists supported by Russia. And it used Iraq in a proxy war against Iran, is also supported by Russia.

Basically, the US invaded Iraq because it had to invade somewhere after the 9/11 attacks. Saudi Arabia was the obvious suspect, given their funding of fundamentalist Islam generally, and Al-Qaeda specifically. Plus the fact that most of the attackers were Saudi.

But that was unworkable, for many reasons. Afghanistan was the other obvious target, but everyone knew that it would be a morass. Given Russia's experience, for example. Or Britain's, back in the day. Plus the fact that most of it had already been pounded into sand.

So Iraq was the perfect target. With lots of juicy stuff to destroy. And an ineffectual military.

Another goal was demonstrating US military hardware. Advertising, to increase sales.