One must ask: Is it ever morally permissible to promise not to do something? Clearly, if it something that I have no moral right to do in any case, then such a promise is superfluous. (Why promise not to steal, when I am already bound by the moral law not to steal.)

If I can promise not to do something that otherwise it would be moral for me to do, then
I am allowed to bind myself not to exercise certain rights.

This seems to me obvious.

The “right to life” is a different sort of thing than, say, the right to property. My property rights mean that you cannot take my property. I can, however, decide to give you my property, in which case it ceases to be my property. That is not an “alienation” of of my property rights, but an exercise of them. If it was my property, it was mine to give away.

Life is different. You cannot kill me, but neither can I authorize you to kill me.

It is kind of misleading to say that I have a “right to my life” in the same sense that I have a right to property or to speech or to marriage.
I have a right to speak or not to speak, to possess my property or to give it away, to marry or not to marry. I do not, however, have a right to live or not to live. My “right to life” is better understood as an obligation on everyone (including myself) not to kill me.

It seems, then, that the word “right” is used in two ways. (a) There are rights (such as the right not to be murdered, not to be raped, etc) which are really better thought of as prohibitions (not to murder, not to rape, etc.) (b) There are rights to do or not to do certain things (speak, marry, have property).

I suppose one could think of type (a) “rights” as “inalienable”. But that seems a somewhat backwards way to speak about moral prohibitions.

Precisely the difference between simple and solemn vows is that solemn vows operate “in rem.” A simple vow of perfect and perpetual chastity renders marriage illicit; solemn profession renders it void.

Similarly, in France, until 1789, a solemn vow of poverty meant that a person could not acquire title to property, by inheritance, or inter vivos and this was true of the law in most Catholic countries. Hence, religious were said to be “civiliter mortuus,” dead for civil purposes.

In England, one of the earliest examples of a trust was when one Ricardus Le Muliner gave a house and garden to Oxford town council “ad opus fratrum” [to the use of the (Franciscan) friars] whose rule forbade them to own property. The pious testator hoped to avoid the prohibition, by vesting the legal title in the council, with a mere moral obligation to let the friars use it.

So these do appear to be cases of the relinquishment of the right itself.

I may also bind myself by a vow to perpetual silence, or perpetual celibacy, or poverty. Those are vows never to exercise certain natural rights. As long as the vows are freely made, my rights have not been alienated.

I may have a right to do something and also a right not to do that thing — including the right to decide never to do it.

The supposed “problem” is illusory.

If we have a pass to alienate our unalienable rights for religious reasons, can we do it for other reasons? What about indentured servitude? Military service?

Did John Locke ever think through whether the vows of obedience and poverty a sister in a monastery makes to her abbess is legitimate within his political philosophy? Or whether it is a good thing to lay down one’s life for a friend? I kind of doubt it.

These political theories seem necessarily limited to a narrower horizon. They are really assertions about the proper limits of government, rather than metaphysical truth claims.