This is a fair question, and helps clarify the position.
I think that most folks do indeed accept that a fundamental basis of all of our rights is a basic belief that we have the right to liberty of person. That is, you have the right to control your own body. I think this is generally a fundamental basis for all of our other rights, but in terms of the constitution, it’s most directly codified in the 14th amendment, under the umbrella of “liberty”.
Now, like most rights, it is not absolute. In terms of the 14th amendment, this limitation is laid out by the due process clause. That is the government is able to restrict your liberty, as long as you have due process. But this does not only mean procedural due process, but also substantive due process. That is, the government is not allowed to make arbitrary restrictions on your liberty, and instead there must be a substantive benefit to society that is provided by that restriction of liberty.
So, for something like vaccines, a mandatory vaccine can be justified because, while it constitutes a limitation on your liberty, that limitation is bound by due process. By forcing you to be vaccinated, it benefits society as a whole, in a very direct way.
For things like drug criminalization, I would offer that there is little substantive reason for drug criminalization laws, as after being in effect for decades, there is little if any empirical evidence of them being beneficial to society. Indeed, there’s a great deal of evidence to the contrary. Thus, I would argue that such laws violate the due process clause by restricting your right to liberty, without substantive due process.
Likewise, another aspect of liberty is liberty of contract. Again, not absolute, but a right none the less. The government cannot arbitrarily limit your ability to enter into a voluntary contract with another person, unless there is some substantive benefit to society. For a while, this notion was even stronger than it is now in Constitutional law, preventing most wage laws, but then in the early 1900’s some case with a hotel worker established that there was a legitimate benefit to society from limiting that right through minimum wage laws.
Now, the right to liberty of person and contract is a limited right, but it is still a fundamental basis for our entire notion of rights, which was my original point. That’s why it’s codified in the 14 amendment as it is. We have a right, albeit a limited one, to liberty. And that includes being able to do what you want to your body, and buy things that you want to.
In cases where the government wants to infringe on that right, it needs to provide a substantive reason for why that restriction will benefit society.
In the case of a mandatory vaccination, I think that reason is fairly clear, and given that there is no real liberty being yielded (since the supposed dangers of vaccinations are generally all fictional), it makes a fairly clear choice to me.
But in the case of legally preventing a person from undergoing a treatment which may hurt themselves, but no one else? And voluntarily entering into a contract waiving their ability to sue people for the outcome of this voluntary action? I do not believe there is a legitimate argument for there being a benefit to society for that restriction on their liberty.
Now, that last part can be discussed and argued, as whether there is a substantial benefit to society involves perhaps some amount of opinon. But my initial rejection was of the notion that you do not have a right to liberty of person or contract, and this is factually incorrect. You do indeed have those rights, not only a fairly fundamental basis for our entire system of rights (such rights generally exist in most modern legal frameworks in some form), but actually as codified in the US constitution. Again, those rights are not absolute. But they certainly do exist.