I see what you are saying, but the same logic implies that there is no vital need to imprison animals, considering that the vast majority of people can get their sustenance from plant based products more efficiently.

However, I would personally argue that a rights based system only works when you have a way to have rights clash and reach compromise positions. An open ended right is not very useful because just about every right becomes impossible to enforce or provide at the extremes. When you provide certain agreed upon rights to both humans and orangutans you can have meaningful discussions about where those rights intersect and how those confluences should be handled, and in this way you avoid the absurd implications of absolute rights.