Unfortunately, I can't say whether it was the right decision to go into Iraq at the time. It really depends on who you believe this administration knew at the time. Sadly, that belief is usually based on your politics, not the other way around as it should be.
If you believe Bush looked at the information he provided and determined Iraq was a threat, then to me his actions were justified. I believe that. Why? Because most of the world believed Saddam had WMD, we knew for a fact he was supporting terrorists, and we knew he desired harm to come to the US. Therefore the logical extension of that that information takes us to Iraq being a threat.
If you believe Bush trumped up the information to justify an attack on Iraq, then you obviously don't think it was justified. If that's the case, someone had better start impeachment proceedings.
What someone believes now isn't as relevant to the discussion. Now we have hindsight. It's easy to say what you would have done then if you knew what you know now.
I liken our invasion of Iraq to a search warrant. Then again, I'm somewhat of an isolationist. I think we had probable cause to go in and search. However, once we determined there was no cause, every last boot should have left the ground. We aren't nation builders. At least we shouldn't be.
