If I want to take my completely legitimately obtained money and obfuscate its source by putting it in a pool with people I have no knowledge of or connection to, I don't see why it should be assumed that I believe these people's intent is to launder the proceeds of some sort of illegal activity and not other people like myself. I think it's even more of a stretch to say that I would know that I'm facilitating someone else's money laundering in that case. There are completely legitimate reasons for wanting to obfuscate one's transaction history, just like there are legitimate reasons for wanting to use an email aliasing service, VPN, etc.