Many libertarians don't mind the fact that drugs are illegal, so much as they mind the fact that the government goes way outside its constitutional authority in its efforts to "ban" them [actually the real efforts are usually to get as much money and power as possible from drug bans].
Many liberarians' biggest problem with drug laws is that they require the police to actively and intrusively seek out criminal violations. This is quite the opposite of the normal police role, which is to respond to criminal complaints.
If a drunk is staggering down the street and making a nuisance of himself, most libertarians would not object to his arrest: he is bothering people, and police don't need to intrusively search him out: his actions are readily observable to all. The situation is much different, however, if someone is smoking dope in his house and waits inside until he sobers up. In that case, the only way the police could ever find out that a "crime" was being committed is by using intrusive surveillance.
Many libertarians would have no objection to the police shutting down a drug house which is creating a clearly identifiable public nuisance. What they object to is intrusive police surveillance and raids on people's homes on the suspicion that they 'might' be dealing drugs. If nobody's complaining, why should the government care?
I see your point, we in Democrap land have voted in an initiative that require our police to never leave the donut shop unless given a call for service. It must be the same way where you live. I note that the drunk driving arrest have gone down to zero even though the drunk driver death rate is up 130%. My big problem here is that the donut shop is 5 minutes from my house and the average home burglary only takes 3 mins.< /sar>
I wonder why they call them patrol cars?