Blair did not lie IMHO, he committed fraud as he was selective of the evidence he gave parliament. Deceiving people by omission, certainly in corporate terms, is known as fraud.
However, Blair was dammed if he did and dammed if he didn't. Not doing anything would have given Saddam the green light to do whatever he wanted. Furthermore, if Saddam was still there he would been probably overthrown by ISIS by now and had Saddam developed WMD, they might be in the hands of terrorists and the world would be a far more dangerous place than it is now.
On balance and in hindsight, what Blair did was probably right, but how he did it was, and still is the issue. What also needs to be remembered is that all major party leaders voted with the government for war. They would have been party to the same intelligence and all came to the same conclusion. Saddam had a track record using WMD on his own people and could not be trusted. Blair belived the JIC in that Saddam had WMD, and if Blair had waited and Saddam had developed his WMD, our armed forces and other armies fighting in the region may well have been obliterated. However, Blair didn't follow Thatchers' advice that when you form a War Cabinet you do not invite your Chancellor. He clearly let the troops down by not equiping them properly.
Nevertheless, I think the lesson that needs to be learnt here is that when we send British troops into a combat zone, money should not be an issue. They must be the best equipped troops in the world. Additionally, stratigy must be planned, objectives including an exit stratigy are tantamount to a successful outcome and set out from the start. Personally I think that it ought to be legal for Regime Change to be reason for war but I know many will disagree. Some people are far to dangerous to be allowed to destablise the world in which we live in, particularly when the have a track record similar to Saddam.