Almost everybody seems to now agree; the second Iraq War (started in 2003 with the intention to force regime change in Baghdad, and still ongoing as a civil and sectarian war with heavy foreign involvement) was a grave mistake at best and an illegal, unnecessary and immoral act at worst. The war resulted in the deaths of untold numbers of Iraqis and thousands of coalition troops, and poisoned the legacy of every politician involved. The publication of the Chilcot Inquiry report in the UK has all but assured that Tony Blair will go down in British history as first and foremost a failed war premier.
I've found exactly one major and serious argument on the other side of the debate, by Columbia law professor Philip Bobbitt. He emphasises the perception of Saddam Hussein's regime in the days when the decisions to invade (by the US), and to participate (by the UK and Australia in particular) were made. Occupying a political and diplomatic ringside seat next door in Kuwait in the run-up to the war during 1998-2002, I want to further explore this historical perception.
In October 1998 US Congress passed and President Bill Clinton signed into law the Iraq Liberation Act,making it official US policy to 'support efforts to remove the regime headed by Saddam Hussein from power in Iraq' (George H. W. Bush had refused to do the same in 1991 during the Gulf War). Clinton followed up two months later with Operation Desert Fox, a four-day bombing campaign against military targets in Iraq, after a particular egregious breach of the UN arms control regime by Saddam.
Evident in hindsight, at the time nobody knew for sure the extent of Saddam's WMD program. That included all UN experts working within Iraq, many of whom regularly came to Bahrain (many expats from Gulf countries, including diplomats, visited the country for legal booze and a semblance of nightlife). In the years after Desert Fox it was an open secret for anyone in Kuwait who really wanted to know that a US build-up to war was underway. When and how, nobody could say (including presumably the US planners themselves). But the military means transported over the following years to the sprawling US base adjacent to Kuwait International Airport clearly went beyond building up a tripwire in the country (in case of an eventual return by Saddam to what he still considered Iraqi territory).
The fear of another Iraqi invasion was still very much alive in Kuwait at the time. Not even ten years after the liberation of the country, Kuwait's graveyards were terrible reminders of the occupation Saddam had imposed on its tiny neighbor following the invasion in August 1990. There was not a single family in in the country that hadn't experienced of illegal arrest, robbery, torture, high-jacking and/or outright murder at the hands of Iraqi goons during their nine-month occupation.
So when the Americans and their allies started their sweep of Iraq in March 2003, almost every single Kuwaiti (including many of the fiercest anti-American Islamists) jumped for joy. The raw fear of seeing their country disappear from the map was finally alleviated.
Many other points and responsibilities for the Iraq war are of course far more complex. When and how the war was started, the terrible squandering of opportunity by the US and sectarian Iraqi politicians after Saddam's eviction, and the massive foreign interference in Iraq from both Iran and the conservative Sunni alliance on the Gulf are entirely different stories. But at the time and on the ground in Kuwait there were very real reasons to remove Saddam: to bring help to the long-suffering Iraqi people, and to bring security to the country's neighbours and of the rest of the world.