> Although I think weed should be legal, in the mean time I am not interested in my taxes paying for the confinement or deportation of Canadians. Ergo, one can support weed legalization and also believe that weed consumption can be used from a practical perspective to deny entrance to foreigners.

This makes no sense. How does having consumed weed in the past entail that one will consume weed in the United States? This is like saying that a person who has driven on the left in the past will drive on the left in the United States, and should therefore be denied entry. It's ridiculous.

I think driving on the left is a false analogy. We don't drive on the left because we enjoy it or because it makes us happy. However, if we have consumed weed in the recent past, that is a strong signal that we have a preference for weed and would pursue the experience again in the future.

If you and I had a betting market that allowed us to bet on an individual's likelihood of consuming weed while in the United States, knowledge of that person's past behavior in consuming weed would be a strong piece of evidence that you could use when making a bet.

Anybody consuming weed today is more likely to have consumed it in the last 30 days than somebody that is not consuming weed today.

So what probability do you assign to someone smoking weed illegally in the United States, given that they have smoked weed in a different country where it's legal?

I wonder if border screening is cheaper than just deporting convicts back to Canada?

Of course making actual behavior consequential rather than potential behavior doesn't have those delicious authoritarian overtones.