That's hard to say, and given what we believed at the time, there certainly were good reasons to invade.
As for building democracy, it has become a useful goal when we've been involved in countries for other reasons (for instance, Germany or Japan), but on its own I doubt many would consider it a good reason for significant military operations in a country. Since we're in Iraq already, we should ceratinly make every effort to promote a stable government, but the goal of a stable government wouldn't have alone provided a sufficient reason to enter the country in the first place.
That's an opinion. Not the only one but an opinion.