I can't speak for all of the Linux community, but I can speak for myself. I want to see a future where people have more freedom in how they use their computers, and this freedom is often threatened by big corporations (particularly microsoft) which control both the software itself and the rights to use this software. These are real issues which really affect people's lives, even though it is often not obvious.
I will say right up front I do not take the Richard Stallman line that all software must be 100% free 100% of the time, and if not we should not use it. This is simply not pragmatic, for reasons economic, political, and technical. However, I DO think software freedom is important. How many times have companies tried to claim things such as the right to tell users what they're not allowed to do with their software? Or tell users that they now own the users' data (think facebook)? Or tell other companies they are forced to pay for software they don't actually buy (microsoft to OEMs)? Or give government agencies tools to spy on customers (Windows NSA backdoor)? Or promised to deliver the votes of a county using its voting equipment to the company's favored candidate (Diebold in Ohio, 2004)? I am a law student, and these issues are rarely brought up in law school because most lawyers are not terribly computer-savvy, but these types of issues are huge in all other areas of law. If a power company tried to tell customers they weren't allowed to use the grid for, say, powering video recording equipment (because the same company owned a TV station and feared competition) or recharging vibrators (because it offended the power company's morals) the legal community would be up in arms, the case would go to court, and the company would be barred from imposing such constraints. Yet software companies do equivalent things on a regular basis. Not to mention sending massive lobbies to Washington to influence federal policy. For me the bottom line is, the more we use Linux, the less control Microsoft and its ilk are able to exercise over society.
So yes, I think a future with much greater Linux desktop share is worth working for. Notice that I say much greater; I do not aim for 100%. As you say, everyone having their favorite is important, and it IS all about choice. So nobody should be coerced into using Linux, but I *do* weigh in with my opinion of why it is better when the topic arises. Of course, the community DOES need to address many usability issues, and does need to consider desktop users important; IMHO these technical and documentation tasks are more important than proselytizing to the uninitiated. The community also needs to be brutally honest about what Linux can and cannot do. I will never tell anybody that Linux is easier to use than Windows for all types of tasks on all types of computers. However, in complete honesty, I find it easier to use for about 90% of my tasks. YMMV. I have also been using Linux for 10 years now, and have seen configuration go from a nigh-impossible, monumental undertaking to most things working out of the box. On my first Linux box I had to recompile the kernel just to get sound working; the last 6 times I have installed Ubuntu, on Dell and Gateway notebooks, sound, wifi, printing, webcams and basically all other hardware Just Worked (TM) on the first try. Last year I installed Xubuntu on my Dad's decade-old laptop, because his Windows install was so virus-ridden he could never get any work done (and resisted all my attempts to fix it). Now it's true that when synaptic tells him something is broken and he needs to "sudo dpkg blah-blah" on the command line he has to call me, but this has happened exactly once in the last year, which is less than the times he had to call me with Windows issues he found incomprehensible. So I think Linux truly is a better choice now for many average users, we will (and must) continue to make it work even better and for more users, and a world with more free software is worth fighting for.