Ultimately I agree that the West absolutely should not have invaded Iraq, although these observations are much more easily made in hindsight

The West should have invaded Iraq

• The dictatorial regime under Saddam Hussein committed human rights abuses against their own people and invaded other nations in defiance of international law, which it can be argued should be stopped at all costs.
• He terrorized and killed hundreds of thousands of Iraqi's since he took power in 1978.
• He violated the conditions of the US-led UN cease-fire following his illegal invasion of Kuwait, by firing upon allied planes who were enforcing the agreement, and stopped allowing UN inspections for several years beginning in 1998.
• It is easier to see in hindsight that some of the information was false, but in a post-9/11 environment people were terrified and overly cautious so the threat seemed justified at the time.
• There were reports that Iraq had in fact did have weapons of mass destruction (WMDs): ongoing biological, chemical, and nuclear weapons programs, another violation of the ceasefire.
• The normal diplomatic tools had repeatedly been tried and failed - since 1991, Saddam had ignored 17 different U.N. resolutions.

The West should not have invaded Iraq

• Saddam Hussein had destroyed all WMDs as a part of the initial ceasefire.
• No WMDs were ever found following the US invasion of 2003.
• Economic sanctions placed as a solution to the invasion of Kuwait and the original US intervention severely harmed the country and led to a health crisis in which thousands of children were dying each month.
• It is speculated that Iraq's threat was exaggerated in order for the US to gain control of an important Middle Eastern, oil-producing state.
• The majority of intelligence used to justify the invasion, such as reports of WMDs and links to 9/11 and Al-Queda was completely based upon false pretences.
• The UK chose to join the invasion before peaceful options had been exhausted, as was found in the Chilcott Report.
• The report also determined there was no imminent threat from Saddam -
  Iran, North Korea and Libya were considered greater threats in terms of nuclear, chemical and biological weapons proliferation.
• The invasion was rushed so militaries were ill-equipped for the task leading to many preventable deaths as well as factions having to strike deals with enemy militias.
  -Several governments including the UK had no post-invasion strategy.
• The UK did not achieve its objectives, so the invasion was not considered successful.
• The war was extremely costly, costing £8.4bn in the UK and $2.4 trillion in the US.
• It cost the lives of between 184,382 and 207,156 civilians in just 7 years, compared to 250,000 at the hands of Saddam over 24 years.