Uncheck money laundering is a huge deal. It is by and large used for criminal and/or politically motived (IE: terrorism or otherwise) operations. One of the core methods that holds organised crime at bay is the government's ability to constrict their money supply. You can only get so large as an organisation if you do all your transactions in cash.
What is the real evidence that this is true?
As I've noted before, what is the magnitude of terrorist related transactions? And is there any evidence that these AML laws actually inhibit transfers for such people?
I consult to financial institutions in anti-money laundering, so I feel I can speak to this with some knowledge:
Money laundering is a huge deal, but not for terrorism. Terrorist financing is actually different - it's moving legitimate funds for an illegitimate purpose, rather than the other way around - and there is still not an effective scenario to monitor for it. 9/11 they think cost around $20k to execute. The numbers are too small.
The "lazy policing" argument I disagree with: I don't know the numbers, but I'd suspect a large proportion of murder convictions are from people not actually witnessing the murder, but someone found to be disposing of the body, hiding the murder weapon, basically everything that is a result of killing someone. ie the results of the crime, rather than the crime itself.
How money laundering does cause a problem though is it disrupts the economy. For example:
I want to move $20 million to my partner in crime overseas. I can't wire him $1 million without someone seeing that: what I can do, is send him 2000 laptops and charge him a dollar per laptop. He now has an invoice showing he's paid for these laptops, and he can sell the laptops at a reduced price to move them quickly and now has his $1 million. He has also now undercut every other laptop seller in his marketplace. This may put legitimate businesses out of business.
Same goes for any other business propped up by illegitimate funds. They compete with legitimate businesses without valid business models. Depending on the amount of laundering or the size of the community, it can do huge damage.
Legislation in the US however (USA PATRIOT act) was pushed through with an emphasis on terrorism as it was the hot topic (2001). It's generally believed in the industry that this was to cut down on tax evasion (which itself is a crime and you can debate how bad that is for years), but saying that money laundering doesn't cause problems in itself is incorrect.