Sometimes I hear the allegation that to claim that voting is not obligatory is to disparage the value of democracy. If democracy is a valuable institution, everyone ought to vote.
But this simply doesn't follow. Hospitals are valuable institutions, but volunteering at a hospital is not obligatory. Fire departments are valuable institutions, but serving as a volunteer fire fighter is not obligatory. I believe that we're obligated to make substantial philanthropic contributions when we can, but what specific form this contribution ought to take will depend on a variety of considerations.
In particular, we ought to think carefully about how much good we can expect different kinds of contributions to do on the margin. If your local fire department has more volunteers than it can handle but the hospital is in desperate need of help, that's a good reason to volunteer at the hospital. The decision to allocate your time and effort to the hospital in no way disparages the value of fire departments.
In the same vein, if you don't expect the time and effort you would spend preparing and casting a wise vote to do any good, then you have reason to use that time and effort on other causes that will do good. This decision to not participate in the democratic process no more disparages the value of democracy than your decision to volunteer at the hospital disparages the value of fire departments.