It isn't robbery as defined by the law like the death penalty isn't murder either legally. From a philosophical point of view though, opinions defer. Not saying I agree or not, just saying.
I'm still not comprehending how telling someone not to do something would amount to confiscation of property. State mandated confiscation of property would be comparable to robbery the way that legal death penalty would be comparable to murder, but no confiscation of property seems to be involved in simply telling people that some things are not allowed (I'm avoiding here, of course, the very issue of whether it's wise to do that in the first place, which it probably isn't, at least for the foreseeable future.)
The property used to commit a crime are usually taken by the police. What do you think happens to your meth lab if you get caught? Or your stock of marijuana or raw milk or the other gazillions things you are forbidden to sell by the power that be and knows better what's good for us?
The police can't do any such thing here. Only a court could. And even then, it generally happens to the property that is the result of a crime (like bribes, for example, or drug money). What message about the level of respect towards private property and human rights would it send if unrelated property was seized for no good reason? If you can't sell your raw milk (I don't actually believe it's illegal here anyway), I don't think anyone is going to take it from you. After all, it's better if you have to get rid of it. You're perfectly free to drink it. At least the state doesn't have to pay for its sanitary disposal.