What if the police asked for the names of everyone who discussed using cannabis in their email exchanges? Would you really argue that in states where cannabis u

What if the police asked for the names of everyone who discussed using cannabis in their email exchanges? Would you really argue that in states where cannabis use was illegal that it would be perfectly okay to do this, collect just the names of people who had used mentioned cannabis in email and then visit their homes to question them further about this? I'm pretty surprised how many people on HN seem to find this acceptable when this is clearly a form of dragnet surveillance.