The Iraq War wasn't about installing democracy. After 9/11 the US was in a shocked, irrational state of mind. I would hope other nations would behave differently given the same situation and power, but I have my doubts about that also.

There was a shortage of enemies to punish, so Saddam Hussein was the next best villain. After all, he did not only have weapons of mass destruction previously, but also used them.

I actually live in a country where regime change worked emphatically well (Germany). I can't recall any such "regime change" project though were the major intent was to install democracy. In Iraq it was the WMD pretense and a diffuse sense of retaliation. In Libya it was to stop an army from shelling civilian living quarters. Mostly the intention is "just stop killing people, dammit!" And it actually works. You can never say for sure, but for example if Syria is any indication, it worked in Libya. While there are tons of problems in Syria, continued shelling and bombing of civilians isn't one of them any more.