Even if there weren't any WMD, the ISG found plenty of documentary evidence to prove that Saddam was embarking on a strategy of re-armament in breach of SC resolutions.
(1) There were no WMDs.
(2) What they found were plans. There was no evidence that SH was capable of acting upon those plans and, even if he was had been able to do so, the weapons wouldn't have been a threat to either the UK or the US
(3) Breach of SC resolutions has never been a legitimate ground for invasion - you need a second resolution authorising action. This breaching resolutions argument makes absolutely no sense - no lawyer who has any genuine expertise in international law has ever endorsed that position (in fact, the deputy legal chief at the foreign office resigned because she felt so strongly over how flawed the UK's argument was)
Personally, in hindsight I very much agree that the reasons we went to war were flawed. Primarily due to the intelligence received but what can you do.
I think to call the evidence on which the dossier was based as intelligence 'received' is stretching the meaning of that word a little too far - part of it was invented, part of it was effectively taken from a flimsy report written by someone who had no expert knowledge of the situation.