>If an officer came to you and said, "Here is a photo of a 12 year old girl who was kidnapped and sold as a sex slave. The payments were all in bitcoin and we would have caught the criminals involved if they had not used your service to hide their transactions."
They'd just use cash. The argument against anonymous transactions and tumblers is the same as the argument against cash. Besides, this kind of emotional blackmail is the reason people avoid talking to the police.
While true, criminals dislike getting ripped off just as much as normal people and have a wider variety of remediation techniques at their disposal. Cash pipelines are really really hard to manage without losses and/or disclosing identifiable/traceable information.
They'd just use cash. The argument against anonymous transactions and tumblers is the same as the argument against cash. Besides, this kind of emotional blackmail is the reason people avoid talking to the police.