>>I clearly remember how all that WMD stuff was obvious
propaganda at the time.

Interesting, do you have references?

LA Times opinion piece explicitly calls out the evidence about Iraq as propaganda:

http://articles.latimes.com/2003/jan/05/opinion/op-marshall5

The Christian Science Monitor discusses propaganda that was used to sell the first Gulf War, and warns us about the dangers of propaganda about the situation with Iraq in 2002:

http://www.csmonitor.com/2002/0906/p25s02-cogn.html

The Guardian reports that much of the British evidence for invasion is based not on new intelligence, but cherry picked academic articles and years old intelligence. This is before the invasion:

http://www.theguardian.com/uk/2003/feb/08/politics.iraq

Hans Blix reports that no evidence of proscribed activities has been found in Iraq. While he qualifies it that Iraq has not been as cooperative as wished, he believes that the disarmament plan can be completed within a few months given the recent extra pressure. This is also before the invasion:

http://www.cnn.com/2003/US/03/07/sprj.irq.un.transcript.blix...

You would naively/cynically assume that if the US army/etc
knew they wouldn't find any remaining WMD programs, they
would be planted?

It's not exactly that there were people who knew they wouldn't find any remaining WMD programs, and went ahead anyhow. It's that strong incentives were set up to find evidence that there were WMDs in Iraq, so the evidence presented was weighted much more heavily towards that which found evidence of WMDs or attempts by Saddam to make or buy WMDs.

This was written shortly after the invasion, about how the Bush administration didn't like the intelligence it was getting from the CIA, so it set up its own Office of Special Plans, specifically tasked to find evidence of WMDs in Iraq and ties to Al Qaeda:

http://www.newyorker.com/archive/2003/05/12/030512fa_fact

Well, when the entire purpose of your organization is to find evidence of a particular fact, you will probably find such evidence. That doesn't mean it's true; just that enough dedicated people can find evidence for it. And since you can never conclusively provide evidence of the absence of a WMD program, especially since Saddam wasn't always fully cooperative with inspectors, it was fairly easy to get carried away providing evidence that he had or was developing WMDs, without paying sufficient attention to any counter intelligence.

And of course there's the Downing Street Memo, from July 2002 (nearly a year before the invasion) that reveals that the decision to invade was a fait accompli and the main point of the intelligence and inspections after that point that were just used to provide better political support for the invasion:

https://en.wikipedia.org/wiki/Downing_Street_memo

Also, not that the didn't have to plant evidence of WMDs in Iraq after the invasion; people found out that there were no WMDs, found out about the Downing Street Memo, and yawned. The media didn't care; the US media barely reported on the Downing Street Memo. The public and politicians didn't care; after September 11th, there were still enough people who thought that "something had to be done", and people who thought that Saddam had ties to Al Qaeda, that there was very little political push against the war.

That's what gets me the most about this; how very apathetic the American public and American politicians have been about the mass slaughter of Iraqis (including thousands of civilians), torture, indefinite detention without trial in Guantanamo, extrajudicial assassination on US citizens, and so on and so forth. It's chilling to think that so few people care.