A strong argument for individuals having complete freedom in decisions affecting nobody else is that each person has much better information about what they want and the details of their situation than anyone else does or could. For example it is often argued that people should choose for themselves how much fat to eat without government intervention, as they have intimate knowledge of how much they like eating fat and how much they dislike being fat, and what degree of mockery their social scene will administer and so forth. Not only that, but they have a much stronger incentive to get the decision right than anyone else.
A counterargument often made here is that people are just so irrational that they don’t know what’s good for them. Sometimes it’s not clear how anyone else would do better, being people themselves, and people in complicated organizations full of other motives no less. Sometimes it’s not clear whether people are actually that irrational in real life, or if they manage to compensate.
However one situation where it seems quite likely that other people would be better informed on your preferences and how an outcome will affect you is when you are making decisions that will affect you far in the future. The average seventy five year old probably has more in common with the next average seventy five year old than they have in common with their twenty five year old selves, at least in some relevant respects. The stranger people are the less true this is presumably, but most people are not strange. So for instance a bunch of old people dying of lung cancer have a much better idea of how much you would like lung cancer than you do when you are weighing it up in the decision to smoke or not much earlier in life.
This might not matter if people care a lot about their far future selves, as they can of course seek out people to ask about how horrible or great which experiences are. However even then they are doing no better than anyone else who does that, so there is no argument to be made that they have much more intimate knowledge of their own preferences and situation.
You could still argue that I have much more of an interest than anyone else in my own future, if only a slight one compared to how much my future self cares about herself. But I also have a lot to gain by exploiting her and discounting her feelings, so it’s not clear at all from a utilitarian perspective that I should be free to make decisions that only affect myself, but far into the future.
The simple way to make this argument is to say that the ‘individual’ is temporally too big a unit to be best ruled over by one part in a (temporal) position of power. The relevant properties of the right sized unit, as far as the usual arguments for libertarianism are concerned, are lots of information and shared care, and according to these a far future self is drifting toward being a different person. You shouldn’t be allowed to externalize onto them as much as you like for the same reasons that go for anyone else.