After writing the third paragraph below, it would appear I think your rebuttals to Arguments 4 & 7 are most salient. I believe the idea that fundamental research is very important for future discoveries to be possible, but I have an argument for that which you don't list. The great minds that gave us theories of gravitation, evolution, and quantum mechanics all learned their fields by doing research. Some of them did basic theoretical work, and others did applied work. But, even the ones who did applied work may have learned significantly from people who were more suited, or who more enjoyed, theoretical work.

So, if you really, really love the theoretical stuff, and you're just worried that you'll feel your life has been a waste at the end, being afraid of lifelong commitment is not a good reason by itself to fail to commit. Honest curiosity about other fields is valid, and if that's at least part of what you're feeling, read on. (Well, you may read on anyway, I'm aware :)

What else have you tried doing? Have you ever worked in a position where you did something other than pure research? If the answer is "No," I would say you should definitely value trying something else, at least for a little while. If you are currently a research graduate student, you are in the perfect position to take a year off and do just that. Apply for an internship to do math modeling for an oil company (or work at a radio telescope, or something else that has a practical application.) I did a one year internship at Los Alamos National Labs as a spacecraft payload operator based on my undergrad physics degree. In a "real job," you have several different kind of responsibilities--not just different responsibilities, but different kinds. I checked the daily health reports on the satellite, yes. But I also attended meetings of top astrophysicists, getting insight into how they think and what they do. (One of those scientists, Roger Fenimore, taught me the lesson that the people who really make important things happen often get experience from multiple disparate fields, and then notice important connections between them.) I investigated small failures in the satellite data, learning about materials science and clean room procedures along the way. I gave tours of our facility to visitors. I participated in a student council, helping to improve student life in a small, isolated town.

If you're a professor already, you're in a bit more of a pickle, because there's no guarantee of a place to come back to if you leave. Still, it might be worth the risk.

[26 Feb 2011: Edited for intended generality. I do not think working for an oil company is really your only choice. It's just an example of something a math friend of mine did.]