Do you think that you are too intelligent to be in a cult? Then I would encourage you to look into how any other cult works. They aren't populated by stupid people. Aum Shinrikyo was almost exclusively university professors and graduates. For Pete's sake - they had the know-how and means to make WMDs.

As to Monero, I would encourage you to look at Jonestown mass-suicide. You know why Jones killed them all? Because he was afraid he is loosing control over them. People like that will burn everything around them rather than give up control. Being smart doesn't make you immune to being in a cult. This is the most valuable lesson Monero taught me.

I can tell you why you can't stop the 'spam'. You are thinking in cult doctrine. If it was real spam, and I was selling Viagra for example - you could easily ban keywords and urls. Instead, stop being a sheep, think like a cult leader. Recoginse that this 'spam' is just some bullshit that you tell to the sheep.

When you do that, solution will present itself. Observe. 'spam' -> 'FUK talks bad things about Monero on our IRC' (Don't say that out loud obviously, that will get you excommunicated) Solution? Get off-the-shelf sentiment analyser, detect anyone who 'talks bad things about Monero' and ban them.