Anything that we enact into law is "lawful", it's circular reasoning. It doesn't say anything about the ethics of the situation. If 80% of people agree democratically to murder the other 20%, it will be lawful, but does it suddenly become ethical? And if they change the word so that it's "lawful execution" does that make it OK?
In the same vein, I'm using the common definition of "robbery" without any legitimizing window dressing. I'm asking "under what circumstances is it ethical to rob people?" and "under what circumstances is it ethical to enslave them?"
Surely some exist. For instance, being drafted to fight a war and being enslaved are basically equivalent in terms of lived experience. We've decided that yes, in order to defend society against existential threats it's ethical to enslave people. I don't disagree, and would like to point out adherence to the maxim of violating liberty only in direct defense of liberty.
But this does frame the draft to fight WWII and the Vietnam War differently. It's much harder to make the case that North Vietnam was an existential threat to US liberty, so drafting/enslaving people to fight there seems much less ethical.
Following this line of reasoning, the question is "Is it ethical to rob people to pay doctors?". And since lacking a doctor doesn't deprive anyone of liberty, the answer must be "No".
You'll note that all of this can basically be derived from the following (from the Declaration of the Rights of Man)
> 1. Men are born and remain free and equal in rights...
> 4. Liberty consists in the freedom to do everything which injures no one else; hence the exercise of the natural rights of each man has no limits except those which assure to the other members of the society the enjoyment of the same rights...
Taxes are “lawful”, therefore under your framework, they are neither theft nor robbery.
Unless, somehow, lawfulness has nothing to do with laws. In which case what you’re saying is just straight up nonsense.